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 $72.62   3.727%   $75.3265   $75.33   $75.35   $75.30  
  Purchase #2 $217.62   4.672%   $227.7872   $227.79   $227.80   $227.80  
  Purchase #3 $84.86   11.645%   $94.7419   $94.74   $94.75   $94.70  
  Purchase #4 $68.53   10.719%   $75.8757   $75.88   $75.90   $75.90  
  Purchase #5 $56.68   10.764%   $62.781   $62.78   $62.80   $62.80  
  Purchase #6 $122.78   3.402%   $126.957   $126.96   $126.95   $127.00  
  Purchase #7 $227.64   11.761%   $254.4127   $254.41   $254.40   $254.40  
  7 purchase totals = $850.73       $917.8820   $917.89   $917.95   $917.90