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 $64.81   13.241%   $73.3915   $73.39   $73.40   $73.40  
  Purchase #2 $167.96   11.838%   $187.8431   $187.84   $187.85   $187.80  
  Purchase #3 $240.86   4.254%   $251.1062   $251.11   $251.10   $251.10  
  Purchase #4 $235.43   3.733%   $244.2186   $244.22   $244.20   $244.20  
  Purchase #5 $142.65   11.593%   $159.1874   $159.19   $159.20   $159.20  
  Purchase #6 $198.33   13.709%   $225.5191   $225.52   $225.50   $225.50  
  Purchase #7 $202.88   6.580%   $216.2295   $216.23   $216.25   $216.20  
  7 purchase totals = $1,252.92       $1,357.4954   $1,357.50   $1,357.50   $1,357.40