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 $64.39   3.662%   $66.748   $66.75   $66.75   $66.70  
  Purchase #2 $130.60   4.791%   $136.857   $136.86   $136.85   $136.90  
  Purchase #3 $136.99   6.784%   $146.2834   $146.28   $146.30   $146.30  
  Purchase #4 $12.74   12.483%   $14.3303   $14.33   $14.35   $14.30  
  Purchase #5 $212.69   11.829%   $237.8491   $237.85   $237.85   $237.80  
  Purchase #6 $136.78   5.277%   $143.9979   $144.00   $144.00   $144.00  
  Purchase #7 $200.46   5.723%   $211.9323   $211.93   $211.95   $211.90  
  7 purchase totals = $894.65       $957.9980   $958.00   $958.05   $957.90