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 $47.47   12.226%   $53.2737   $53.27   $53.25   $53.30  
  Purchase #2 $67.36   8.118%   $72.8283   $72.83   $72.85   $72.80  
  Purchase #3 $212.89   11.720%   $237.8407   $237.84   $237.85   $237.80  
  Purchase #4 $145.36   10.258%   $160.271   $160.27   $160.25   $160.30  
  Purchase #5 $32.91   6.536%   $35.061   $35.06   $35.05   $35.10  
  Purchase #6 $229.55   7.523%   $246.819   $246.82   $246.80   $246.80  
  Purchase #7 $149.55   6.145%   $158.7398   $158.74   $158.75   $158.70  
  7 purchase totals = $885.09       $964.8335   $964.83   $964.80   $964.80