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 $231.42   11.717%   $258.5355   $258.54   $258.55   $258.50  
  Purchase #2 $177.36   9.692%   $194.5497   $194.55   $194.55   $194.50  
  Purchase #3 $54.37   4.331%   $56.7248   $56.72   $56.70   $56.70  
  Purchase #4 $33.45   13.199%   $37.8651   $37.87   $37.85   $37.90  
  Purchase #5 $33.99   8.103%   $36.7442   $36.74   $36.75   $36.70  
  Purchase #6 $162.97   6.776%   $174.0128   $174.01   $174.00   $174.00  
  Purchase #7 $120.70   3.670%   $125.1297   $125.13   $125.15   $125.10  
  7 purchase totals = $814.26       $883.5618   $883.56   $883.55   $883.40