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 $84.30   12.604%   $94.9252   $94.93   $94.95   $94.90  
  Purchase #2 $92.38   10.742%   $102.3035   $102.30   $102.30   $102.30  
  Purchase #3 $87.98   9.494%   $96.3328   $96.33   $96.35   $96.30  
  Purchase #4 $96.97   4.801%   $101.6255   $101.63   $101.65   $101.60  
  Purchase #5 $43.62   5.605%   $46.0649   $46.06   $46.05   $46.10  
  Purchase #6 $160.71   12.425%   $180.6782   $180.68   $180.70   $180.70  
  Purchase #7 $116.67   3.284%   $120.5014   $120.50   $120.50   $120.50  
  7 purchase totals = $682.63       $742.4315   $742.43   $742.50   $742.40