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 $19.72   3.740%   $20.4575   $20.46   $20.45   $20.50  
  Purchase #2 $11.56   4.862%   $12.122   $12.12   $12.10   $12.10  
  Purchase #3 $39.64   12.180%   $44.4682   $44.47   $44.45   $44.50  
  Purchase #4 $122.80   5.306%   $129.3158   $129.32   $129.30   $129.30  
  Purchase #5 $231.77   8.622%   $251.7532   $251.75   $251.75   $251.80  
  Purchase #6 $228.81   11.349%   $254.7776   $254.78   $254.80   $254.80  
  Purchase #7 $234.44   3.404%   $242.4203   $242.42   $242.40   $242.40  
  7 purchase totals = $888.74       $955.3146   $955.32   $955.25   $955.40