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 $88.87   6.823%   $94.9336   $94.93   $94.95   $94.90  
  Purchase #2 $91.78   9.313%   $100.3275   $100.33   $100.35   $100.30  
  Purchase #3 $237.86   13.677%   $270.3921   $270.39   $270.40   $270.40  
  Purchase #4 $240.48   12.840%   $271.3576   $271.36   $271.35   $271.40  
  Purchase #5 $5.75   3.326%   $5.9412   $5.94   $5.95   $5.90  
  Purchase #6 $139.57   6.756%   $148.9993   $149.00   $149.00   $149.00  
  Purchase #7 $182.58   10.370%   $201.5135   $201.51   $201.50   $201.50  
  7 purchase totals = $986.89       $1,093.4648   $1,093.46   $1,093.50   $1,093.40