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 $118.70   5.116%   $124.7727   $124.77   $124.75   $124.80  
  Purchase #2 $77.69   6.529%   $82.7624   $82.76   $82.75   $82.80  
  Purchase #3 $57.39   13.474%   $65.1227   $65.12   $65.10   $65.10  
  Purchase #4 $188.85   9.591%   $206.9626   $206.96   $206.95   $207.00  
  Purchase #5 $174.75   4.335%   $182.3254   $182.33   $182.35   $182.30  
  Purchase #6 $234.51   12.318%   $263.3969   $263.40   $263.40   $263.40  
  Purchase #7 $64.56   5.367%   $68.0249   $68.02   $68.00   $68.00  
  7 purchase totals = $916.45       $993.3676   $993.36   $993.30   $993.40