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 $85.68   11.188%   $95.2659   $95.27   $95.25   $95.30  
  Purchase #2 $16.51   13.310%   $18.7075   $18.71   $18.70   $18.70  
  Purchase #3 $63.66   5.455%   $67.1327   $67.13   $67.15   $67.10  
  Purchase #4 $56.47   3.585%   $58.4944   $58.49   $58.50   $58.50  
  Purchase #5 $57.44   3.816%   $59.6319   $59.63   $59.65   $59.60  
  Purchase #6 $178.91   12.811%   $201.8302   $201.83   $201.85   $201.80  
  Purchase #7 $66.56   11.545%   $74.2444   $74.24   $74.25   $74.20  
  7 purchase totals = $525.23       $575.3070   $575.30   $575.35   $575.20