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 $22.68   5.551%   $23.939   $23.94   $23.95   $23.90  
  Purchase #2 $35.59   6.107%   $37.7635   $37.76   $37.75   $37.80  
  Purchase #3 $6.65   5.595%   $7.0221   $7.02   $7.00   $7.00  
  Purchase #4 $200.45   10.391%   $221.2788   $221.28   $221.30   $221.30  
  Purchase #5 $158.66   11.544%   $176.9757   $176.98   $177.00   $177.00  
  Purchase #6 $164.25   5.540%   $173.3495   $173.35   $173.35   $173.30  
  Purchase #7 $150.92   3.617%   $156.3788   $156.38   $156.40   $156.40  
  7 purchase totals = $739.20       $796.7074   $796.71   $796.75   $796.70