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 $119.34   4.103%   $124.2365   $124.24   $124.25   $124.20  
  Purchase #2 $68.98   8.374%   $74.7564   $74.76   $74.75   $74.80  
  Purchase #3 $141.99   3.809%   $147.3984   $147.40   $147.40   $147.40  
  Purchase #4 $44.48   9.434%   $48.6762   $48.68   $48.70   $48.70  
  Purchase #5 $104.33   5.793%   $110.3738   $110.37   $110.35   $110.40  
  Purchase #6 $107.32   3.364%   $110.9302   $110.93   $110.95   $110.90  
  Purchase #7 $151.40   12.293%   $170.0116   $170.01   $170.00   $170.00  
  7 purchase totals = $737.84       $786.3831   $786.39   $786.40   $786.40