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 $24.98   5.463%   $26.3447   $26.34   $26.35   $26.30  
  Purchase #2 $211.46   4.113%   $220.1573   $220.16   $220.15   $220.20  
  Purchase #3 $66.37   6.817%   $70.8944   $70.89   $70.90   $70.90  
  Purchase #4 $78.32   11.139%   $87.0441   $87.04   $87.05   $87.00  
  Purchase #5 $79.97   9.201%   $87.328   $87.33   $87.35   $87.30  
  Purchase #6 $68.96   12.127%   $77.3228   $77.32   $77.30   $77.30  
  Purchase #7 $186.64   4.245%   $194.5629   $194.56   $194.55   $194.60  
  7 purchase totals = $716.70       $763.6542   $763.64   $763.65   $763.60