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 $162.95   12.149%   $182.7468   $182.75   $182.75   $182.70  
  Purchase #2 $18.29   4.608%   $19.1328   $19.13   $19.15   $19.10  
  Purchase #3 $53.54   9.773%   $58.7725   $58.77   $58.75   $58.80  
  Purchase #4 $236.48   9.571%   $259.1135   $259.11   $259.10   $259.10  
  Purchase #5 $160.38   8.647%   $174.2481   $174.25   $174.25   $174.20  
  Purchase #6 $237.71   12.708%   $267.9182   $267.92   $267.90   $267.90  
  Purchase #7 $60.58   4.657%   $63.4012   $63.40   $63.40   $63.40  
  7 purchase totals = $929.93       $1,025.3331   $1,025.33   $1,025.30   $1,025.20