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 $206.84   12.288%   $232.2565   $232.26   $232.25   $232.30  
  Purchase #2 $73.38   11.546%   $81.8525   $81.85   $81.85   $81.90  
  Purchase #3 $72.52   13.319%   $82.1789   $82.18   $82.20   $82.20  
  Purchase #4 $13.31   11.648%   $14.8603   $14.86   $14.85   $14.90  
  Purchase #5 $171.38   13.151%   $193.9182   $193.92   $193.90   $193.90  
  Purchase #6 $88.32   5.303%   $93.0036   $93.00   $93.00   $93.00  
  Purchase #7 $175.41   11.231%   $195.1103   $195.11   $195.10   $195.10  
  7 purchase totals = $801.16       $893.1803   $893.18   $893.15   $893.30