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 $88.67   10.856%   $98.296   $98.30   $98.30   $98.30  
  Purchase #2 $115.37   8.653%   $125.353   $125.35   $125.35   $125.40  
  Purchase #3 $25.32   6.769%   $27.0339   $27.03   $27.05   $27.00  
  Purchase #4 $29.35   6.864%   $31.3646   $31.36   $31.35   $31.40  
  Purchase #5 $209.45   7.873%   $225.94   $225.94   $225.95   $225.90  
  Purchase #6 $65.52   12.337%   $73.6032   $73.60   $73.60   $73.60  
  Purchase #7 $45.47   11.198%   $50.5617   $50.56   $50.55   $50.60  
  7 purchase totals = $579.15       $632.1524   $632.14   $632.15   $632.20