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 $88.46   11.171%   $98.3419   $98.34   $98.35   $98.30  
  Purchase #2 $80.41   8.865%   $87.5383   $87.54   $87.55   $87.50  
  Purchase #3 $12.32   11.485%   $13.735   $13.74   $13.75   $13.70  
  Purchase #4 $39.44   12.662%   $44.4339   $44.43   $44.45   $44.40  
  Purchase #5 $80.29   4.129%   $83.6052   $83.61   $83.60   $83.60  
  Purchase #6 $36.56   9.829%   $40.1535   $40.15   $40.15   $40.20  
  Purchase #7 $62.36   3.434%   $64.5014   $64.50   $64.50   $64.50  
  7 purchase totals = $399.84       $432.3092   $432.31   $432.35   $432.20