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 $62.74   11.406%   $69.8961   $69.90   $69.90   $69.90  
  Purchase #2 $162.58   7.671%   $175.0515   $175.05   $175.05   $175.10  
  Purchase #3 $93.94   11.506%   $104.7487   $104.75   $104.75   $104.70  
  Purchase #4 $122.77   11.253%   $136.5853   $136.59   $136.60   $136.60  
  Purchase #5 $177.71   10.574%   $196.5011   $196.50   $196.50   $196.50  
  Purchase #6 $91.38   7.872%   $98.5734   $98.57   $98.55   $98.60  
  Purchase #7 $122.88   5.620%   $129.7859   $129.79   $129.80   $129.80  
  7 purchase totals = $834.00       $911.1420   $911.15   $911.15   $911.20