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 $52.72   13.314%   $59.7391   $59.74   $59.75   $59.70  
  Purchase #2 $74.45   13.674%   $84.6303   $84.63   $84.65   $84.60  
  Purchase #3 $247.39   3.115%   $255.0962   $255.10   $255.10   $255.10  
  Purchase #4 $219.58   9.490%   $240.4181   $240.42   $240.40   $240.40  
  Purchase #5 $93.57   13.548%   $106.2469   $106.25   $106.25   $106.20  
  Purchase #6 $175.37   7.863%   $189.1593   $189.16   $189.15   $189.20  
  Purchase #7 $195.38   5.507%   $206.1396   $206.14   $206.15   $206.10  
  7 purchase totals = $1,058.46       $1,141.4295   $1,141.44   $1,141.45   $1,141.30