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 $241.51   6.301%   $256.7275   $256.73   $256.75   $256.70  
  Purchase #2 $53.87   11.687%   $60.1658   $60.17   $60.15   $60.20  
  Purchase #3 $219.26   5.267%   $230.8084   $230.81   $230.80   $230.80  
  Purchase #4 $216.35   9.436%   $236.7648   $236.76   $236.75   $236.80  
  Purchase #5 $187.33   7.487%   $201.3554   $201.36   $201.35   $201.40  
  Purchase #6 $230.42   10.745%   $255.1786   $255.18   $255.20   $255.20  
  Purchase #7 $101.26   7.260%   $108.6115   $108.61   $108.60   $108.60  
  7 purchase totals = $1,250.00       $1,349.6120   $1,349.62   $1,349.60   $1,349.70