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 $87.54   7.288%   $93.9199   $93.92   $93.90   $93.90  
  Purchase #2 $22.43   12.739%   $25.2874   $25.29   $25.30   $25.30  
  Purchase #3 $64.48   12.832%   $72.7541   $72.75   $72.75   $72.80  
  Purchase #4 $168.56   10.719%   $186.6279   $186.63   $186.65   $186.60  
  Purchase #5 $104.62   5.508%   $110.3825   $110.38   $110.40   $110.40  
  Purchase #6 $200.99   5.247%   $211.5359   $211.54   $211.55   $211.50  
  Purchase #7 $211.90   10.545%   $234.2449   $234.24   $234.25   $234.20  
  7 purchase totals = $860.52       $934.7526   $934.75   $934.80   $934.70