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 $54.80   10.590%   $60.6033   $60.60   $60.60   $60.60  
  Purchase #2 $213.57   13.388%   $242.1628   $242.16   $242.15   $242.20  
  Purchase #3 $101.39   3.300%   $104.7359   $104.74   $104.75   $104.70  
  Purchase #4 $233.72   8.282%   $253.0767   $253.08   $253.10   $253.10  
  Purchase #5 $216.32   5.858%   $228.992   $228.99   $229.00   $229.00  
  Purchase #6 $244.96   9.562%   $268.3831   $268.38   $268.40   $268.40  
  Purchase #7 $101.25   6.661%   $107.9943   $107.99   $108.00   $108.00  
  7 purchase totals = $1,166.01       $1,265.9481   $1,265.94   $1,266.00   $1,266.00