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 $194.56   4.464%   $203.2452   $203.25   $203.25   $203.20  
  Purchase #2 $227.78   4.271%   $237.5085   $237.51   $237.50   $237.50  
  Purchase #3 $199.40   13.335%   $225.99   $225.99   $226.00   $226.00  
  Purchase #4 $148.53   6.287%   $157.8681   $157.87   $157.85   $157.90  
  Purchase #5 $230.93   11.816%   $258.2167   $258.22   $258.20   $258.20  
  Purchase #6 $35.25   5.355%   $37.1376   $37.14   $37.15   $37.10  
  Purchase #7 $238.65   10.530%   $263.7798   $263.78   $263.80   $263.80  
  7 purchase totals = $1,275.10       $1,383.7459   $1,383.76   $1,383.75   $1,383.70