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 $219.68   8.251%   $237.8058   $237.81   $237.80   $237.80  
  Purchase #2 $92.66   12.463%   $104.2082   $104.21   $104.20   $104.20  
  Purchase #3 $155.62   3.247%   $160.673   $160.67   $160.65   $160.70  
  Purchase #4 $90.76   7.694%   $97.7431   $97.74   $97.75   $97.70  
  Purchase #5 $217.57   9.300%   $237.804   $237.80   $237.80   $237.80  
  Purchase #6 $56.97   8.803%   $61.9851   $61.99   $62.00   $62.00  
  Purchase #7 $28.59   3.146%   $29.4894   $29.49   $29.50   $29.50  
  7 purchase totals = $861.85       $929.7086   $929.71   $929.70   $929.70