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 $230.53   6.158%   $244.726   $244.73   $244.75   $244.70  
  Purchase #2 $61.36   8.136%   $66.3522   $66.35   $66.35   $66.40  
  Purchase #3 $17.55   3.274%   $18.1246   $18.12   $18.10   $18.10  
  Purchase #4 $68.99   3.821%   $71.6261   $71.63   $71.65   $71.60  
  Purchase #5 $189.58   7.617%   $204.0203   $204.02   $204.00   $204.00  
  Purchase #6 $44.25   5.417%   $46.647   $46.65   $46.65   $46.60  
  Purchase #7 $56.46   6.308%   $60.0215   $60.02   $60.00   $60.00  
  7 purchase totals = $668.72       $711.5177   $711.52   $711.50   $711.40