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 $50.47   8.574%   $54.7973   $54.80   $54.80   $54.80  
  Purchase #2 $149.67   11.175%   $166.3956   $166.40   $166.40   $166.40  
  Purchase #3 $182.46   11.233%   $202.9557   $202.96   $202.95   $203.00  
  Purchase #4 $63.45   4.552%   $66.3382   $66.34   $66.35   $66.30  
  Purchase #5 $194.64   11.652%   $217.3195   $217.32   $217.30   $217.30  
  Purchase #6 $242.98   4.166%   $253.1025   $253.10   $253.10   $253.10  
  Purchase #7 $163.75   6.845%   $174.9587   $174.96   $174.95   $175.00  
  7 purchase totals = $1,047.42       $1,135.8675   $1,135.88   $1,135.85   $1,135.90