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 $88.95   11.118%   $98.8395   $98.84   $98.85   $98.80  
  Purchase #2 $154.81   8.743%   $168.345   $168.35   $168.35   $168.30  
  Purchase #3 $108.89   4.843%   $114.1635   $114.16   $114.15   $114.20  
  Purchase #4 $34.43   13.874%   $39.2068   $39.21   $39.20   $39.20  
  Purchase #5 $92.57   4.855%   $97.0643   $97.06   $97.05   $97.10  
  Purchase #6 $66.63   9.320%   $72.8399   $72.84   $72.85   $72.80  
  Purchase #7 $18.91   3.417%   $19.5562   $19.56   $19.55   $19.60  
  7 purchase totals = $565.19       $610.0152   $610.02   $610.00   $610.00