Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $221.88   11.279%   $246.9058   $246.91   $246.90   $246.90  
  Purchase #2 $186.67   13.237%   $211.3795   $211.38   $211.40   $211.40  
  Purchase #3 $126.86   5.858%   $134.2915   $134.29   $134.30   $134.30  
  Purchase #4 $132.91   5.385%   $140.0672   $140.07   $140.05   $140.10  
  Purchase #5 $183.87   8.146%   $198.8481   $198.85   $198.85   $198.80  
  Purchase #6 $230.73   6.582%   $245.9166   $245.92   $245.90   $245.90  
  Purchase #7 $131.59   9.474%   $144.0568   $144.06   $144.05   $144.10  
  7 purchase totals = $1,214.51       $1,321.4655   $1,321.48   $1,321.45   $1,321.50