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 $91.94   5.832%   $97.3019   $97.30   $97.30   $97.30  
  Purchase #2 $188.67   9.308%   $206.2314   $206.23   $206.25   $206.20  
  Purchase #3 $150.77   5.547%   $159.1332   $159.13   $159.15   $159.10  
  Purchase #4 $132.45   5.770%   $140.0924   $140.09   $140.10   $140.10  
  Purchase #5 $201.55   11.460%   $224.6476   $224.65   $224.65   $224.60  
  Purchase #6 $39.83   12.503%   $44.8099   $44.81   $44.80   $44.80  
  Purchase #7 $72.62   10.735%   $80.4158   $80.42   $80.40   $80.40  
  7 purchase totals = $877.83       $952.6322   $952.63   $952.65   $952.50