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 $65.88   3.818%   $68.3953   $68.40   $68.40   $68.40  
  Purchase #2 $13.32   7.215%   $14.281   $14.28   $14.30   $14.30  
  Purchase #3 $93.80   4.849%   $98.3484   $98.35   $98.35   $98.30  
  Purchase #4 $90.89   13.271%   $102.952   $102.95   $102.95   $103.00  
  Purchase #5 $120.78   11.195%   $134.3013   $134.30   $134.30   $134.30  
  Purchase #6 $157.94   7.266%   $169.4159   $169.42   $169.40   $169.40  
  Purchase #7 $60.33   8.776%   $65.6246   $65.62   $65.60   $65.60  
  7 purchase totals = $602.94       $653.3185   $653.32   $653.30   $653.30