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 $61.25   5.348%   $64.5257   $64.53   $64.55   $64.50  
  Purchase #2 $8.64   12.624%   $9.7307   $9.73   $9.75   $9.70  
  Purchase #3 $221.32   11.669%   $247.1458   $247.15   $247.15   $247.10  
  Purchase #4 $104.65   8.788%   $113.8466   $113.85   $113.85   $113.80  
  Purchase #5 $230.77   4.185%   $240.4277   $240.43   $240.45   $240.40  
  Purchase #6 $31.55   12.498%   $35.4931   $35.49   $35.50   $35.50  
  Purchase #7 $65.95   13.146%   $74.6198   $74.62   $74.60   $74.60  
  7 purchase totals = $724.13       $785.7894   $785.80   $785.85   $785.60