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 $198.98   11.699%   $222.2587   $222.26   $222.25   $222.30  
  Purchase #2 $23.79   10.519%   $26.2925   $26.29   $26.30   $26.30  
  Purchase #3 $94.88   6.498%   $101.0453   $101.05   $101.05   $101.00  
  Purchase #4 $244.94   5.790%   $259.122   $259.12   $259.10   $259.10  
  Purchase #5 $173.32   4.776%   $181.5978   $181.60   $181.60   $181.60  
  Purchase #6 $238.45   9.216%   $260.4256   $260.43   $260.45   $260.40  
  Purchase #7 $192.25   4.427%   $200.7609   $200.76   $200.75   $200.80  
  7 purchase totals = $1,166.61       $1,251.5028   $1,251.51   $1,251.50   $1,251.50