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 $85.33   8.568%   $92.6411   $92.64   $92.65   $92.60  
  Purchase #2 $31.29   11.455%   $34.8743   $34.87   $34.85   $34.90  
  Purchase #3 $40.53   13.599%   $46.0417   $46.04   $46.05   $46.00  
  Purchase #4 $156.73   6.737%   $167.2889   $167.29   $167.30   $167.30  
  Purchase #5 $65.54   11.472%   $73.0587   $73.06   $73.05   $73.10  
  Purchase #6 $31.78   5.843%   $33.6369   $33.64   $33.65   $33.60  
  Purchase #7 $237.81   11.812%   $265.9001   $265.90   $265.90   $265.90  
  7 purchase totals = $649.01       $713.4417   $713.44   $713.45   $713.40