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 $109.86   8.363%   $119.0476   $119.05   $119.05   $119.00  
  Purchase #2 $33.71   7.285%   $36.1658   $36.17   $36.15   $36.20  
  Purchase #3 $174.44   6.544%   $185.8554   $185.86   $185.85   $185.90  
  Purchase #4 $227.30   5.575%   $239.972   $239.97   $239.95   $240.00  
  Purchase #5 $135.88   7.733%   $146.3876   $146.39   $146.40   $146.40  
  Purchase #6 $63.82   13.817%   $72.638   $72.64   $72.65   $72.60  
  Purchase #7 $72.48   11.185%   $80.5869   $80.59   $80.60   $80.60  
  7 purchase totals = $817.49       $880.6533   $880.67   $880.65   $880.70