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 $60.96   6.415%   $64.8706   $64.87   $64.85   $64.90  
  Purchase #2 $240.62   10.387%   $265.6132   $265.61   $265.60   $265.60  
  Purchase #3 $200.49   3.607%   $207.7217   $207.72   $207.70   $207.70  
  Purchase #4 $70.92   4.872%   $74.3752   $74.38   $74.40   $74.40  
  Purchase #5 $169.37   11.455%   $188.7713   $188.77   $188.75   $188.80  
  Purchase #6 $226.75   9.281%   $247.7947   $247.79   $247.80   $247.80  
  Purchase #7 $235.96   4.370%   $246.2715   $246.27   $246.25   $246.30  
  7 purchase totals = $1,205.07       $1,295.4182   $1,295.41   $1,295.35   $1,295.50