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 $166.73   11.342%   $185.6405   $185.64   $185.65   $185.60  
  Purchase #2 $119.76   11.184%   $133.154   $133.15   $133.15   $133.20  
  Purchase #3 $31.77   11.767%   $35.5084   $35.51   $35.50   $35.50  
  Purchase #4 $250.43   12.453%   $281.616   $281.62   $281.60   $281.60  
  Purchase #5 $232.59   6.668%   $248.0991   $248.10   $248.10   $248.10  
  Purchase #6 $7.88   5.345%   $8.3012   $8.30   $8.30   $8.30  
  Purchase #7 $116.28   5.164%   $122.2847   $122.28   $122.30   $122.30  
  7 purchase totals = $925.44       $1,014.6039   $1,014.60   $1,014.60   $1,014.60