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 $247.70   3.719%   $256.912   $256.91   $256.90   $256.90  
  Purchase #2 $221.34   6.632%   $236.0193   $236.02   $236.00   $236.00  
  Purchase #3 $82.47   11.868%   $92.2575   $92.26   $92.25   $92.30  
  Purchase #4 $102.29   3.670%   $106.044   $106.04   $106.05   $106.00  
  Purchase #5 $121.39   6.819%   $129.6676   $129.67   $129.65   $129.70  
  Purchase #6 $65.88   9.152%   $71.9093   $71.91   $71.90   $71.90  
  Purchase #7 $119.43   5.667%   $126.1981   $126.20   $126.20   $126.20  
  7 purchase totals = $960.50       $1,019.0078   $1,019.01   $1,018.95   $1,019.00