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 $198.48   13.529%   $225.3324   $225.33   $225.35   $225.30  
  Purchase #2 $231.48   6.414%   $246.3271   $246.33   $246.35   $246.30  
  Purchase #3 $54.71   3.393%   $56.5663   $56.57   $56.55   $56.60  
  Purchase #4 $172.76   7.839%   $186.3027   $186.30   $186.30   $186.30  
  Purchase #5 $192.70   6.416%   $205.0636   $205.06   $205.05   $205.10  
  Purchase #6 $132.40   10.533%   $146.3457   $146.35   $146.35   $146.30  
  Purchase #7 $84.84   4.258%   $88.4525   $88.45   $88.45   $88.50  
  7 purchase totals = $1,067.37       $1,154.3903   $1,154.39   $1,154.40   $1,154.40