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 $59.97   8.507%   $65.0716   $65.07   $65.05   $65.10  
  Purchase #2 $242.90   8.374%   $263.2404   $263.24   $263.25   $263.20  
  Purchase #3 $182.28   9.338%   $199.3013   $199.30   $199.30   $199.30  
  Purchase #4 $55.32   4.126%   $57.6025   $57.60   $57.60   $57.60  
  Purchase #5 $51.43   12.275%   $57.743   $57.74   $57.75   $57.70  
  Purchase #6 $84.78   3.302%   $87.5794   $87.58   $87.60   $87.60  
  Purchase #7 $22.65   4.390%   $23.6443   $23.64   $23.65   $23.60  
  7 purchase totals = $699.33       $754.1825   $754.17   $754.20   $754.10