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 $31.94   5.717%   $33.766   $33.77   $33.75   $33.80  
  Purchase #2 $127.96   11.830%   $143.0977   $143.10   $143.10   $143.10  
  Purchase #3 $115.90   11.552%   $129.2888   $129.29   $129.30   $129.30  
  Purchase #4 $240.76   10.398%   $265.7942   $265.79   $265.80   $265.80  
  Purchase #5 $199.87   8.501%   $216.8609   $216.86   $216.85   $216.90  
  Purchase #6 $164.39   6.357%   $174.8403   $174.84   $174.85   $174.80  
  Purchase #7 $231.41   13.403%   $262.4259   $262.43   $262.45   $262.40  
  7 purchase totals = $1,112.23       $1,226.0738   $1,226.08   $1,226.10   $1,226.10