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 $55.84   10.812%   $61.8774   $61.88   $61.90   $61.90  
  Purchase #2 $224.71   8.410%   $243.6081   $243.61   $243.60   $243.60  
  Purchase #3 $88.38   5.478%   $93.2215   $93.22   $93.20   $93.20  
  Purchase #4 $36.79   7.579%   $39.5783   $39.58   $39.60   $39.60  
  Purchase #5 $213.92   6.478%   $227.7777   $227.78   $227.80   $227.80  
  Purchase #6 $93.55   10.669%   $103.5308   $103.53   $103.55   $103.50  
  Purchase #7 $7.91   6.751%   $8.444   $8.44   $8.45   $8.40  
  7 purchase totals = $721.10       $778.0378   $778.04   $778.10   $778.00