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 $65.94   5.727%   $69.7164   $69.72   $69.70   $69.70  
  Purchase #2 $225.39   12.530%   $253.6314   $253.63   $253.65   $253.60  
  Purchase #3 $146.91   4.409%   $153.3873   $153.39   $153.40   $153.40  
  Purchase #4 $27.94   5.753%   $29.5474   $29.55   $29.55   $29.50  
  Purchase #5 $107.28   9.516%   $117.4888   $117.49   $117.50   $117.50  
  Purchase #6 $10.51   13.301%   $11.9079   $11.91   $11.90   $11.90  
  Purchase #7 $212.45   11.480%   $236.8393   $236.84   $236.85   $236.80  
  7 purchase totals = $796.42       $872.5185   $872.53   $872.55   $872.40