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 $12.36   13.656%   $14.0479   $14.05   $14.05   $14.00  
  Purchase #2 $164.92   3.452%   $170.613   $170.61   $170.60   $170.60  
  Purchase #3 $73.29   7.362%   $78.6856   $78.69   $78.70   $78.70  
  Purchase #4 $221.95   6.148%   $235.5955   $235.60   $235.60   $235.60  
  Purchase #5 $139.95   6.708%   $149.3378   $149.34   $149.35   $149.30  
  Purchase #6 $128.30   4.750%   $134.3943   $134.39   $134.40   $134.40  
  Purchase #7 $209.67   3.113%   $216.197   $216.20   $216.20   $216.20  
  7 purchase totals = $950.44       $998.8711   $998.88   $998.90   $998.80