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 $112.37   12.417%   $126.323   $126.32   $126.30   $126.30  
  Purchase #2 $64.60   4.383%   $67.4314   $67.43   $67.45   $67.40  
  Purchase #3 $187.99   6.778%   $200.732   $200.73   $200.75   $200.70  
  Purchase #4 $79.36   6.620%   $84.6136   $84.61   $84.60   $84.60  
  Purchase #5 $110.79   8.269%   $119.9512   $119.95   $119.95   $120.00  
  Purchase #6 $216.93   7.125%   $232.3863   $232.39   $232.40   $232.40  
  Purchase #7 $94.81   6.364%   $100.8437   $100.84   $100.85   $100.80  
  7 purchase totals = $866.85       $932.2812   $932.27   $932.30   $932.20