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 $55.51   11.503%   $61.8953   $61.90   $61.90   $61.90  
  Purchase #2 $44.58   8.735%   $48.4741   $48.47   $48.45   $48.50  
  Purchase #3 $201.63   11.690%   $225.2005   $225.20   $225.20   $225.20  
  Purchase #4 $171.87   7.147%   $184.1535   $184.15   $184.15   $184.20  
  Purchase #5 $89.94   10.303%   $99.2065   $99.21   $99.20   $99.20  
  Purchase #6 $162.64   6.866%   $173.8069   $173.81   $173.80   $173.80  
  Purchase #7 $7.82   11.832%   $8.7453   $8.75   $8.75   $8.70  
  7 purchase totals = $733.99       $801.4821   $801.49   $801.45   $801.50