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 $93.95   3.119%   $96.8803   $96.88   $96.90   $96.90  
  Purchase #2 $244.50   6.477%   $260.3363   $260.34   $260.35   $260.30  
  Purchase #3 $18.26   12.582%   $20.5575   $20.56   $20.55   $20.60  
  Purchase #4 $186.62   11.310%   $207.7267   $207.73   $207.75   $207.70  
  Purchase #5 $71.32   5.434%   $75.1955   $75.20   $75.20   $75.20  
  Purchase #6 $66.78   6.219%   $70.933   $70.93   $70.95   $70.90  
  Purchase #7 $62.64   13.850%   $71.3156   $71.32   $71.30   $71.30  
  7 purchase totals = $744.07       $802.9449   $802.96   $803.00   $802.90