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 $62.34   4.338%   $65.0443   $65.04   $65.05   $65.00  
  Purchase #2 $229.94   12.351%   $258.3399   $258.34   $258.35   $258.30  
  Purchase #3 $50.43   11.584%   $56.2718   $56.27   $56.25   $56.30  
  Purchase #4 $194.66   4.610%   $203.6338   $203.63   $203.65   $203.60  
  Purchase #5 $165.68   8.507%   $179.7744   $179.77   $179.75   $179.80  
  Purchase #6 $22.37   6.703%   $23.8695   $23.87   $23.85   $23.90  
  Purchase #7 $195.59   5.852%   $207.0359   $207.04   $207.05   $207.00  
  7 purchase totals = $921.01       $993.9696   $993.96   $993.95   $993.90