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 $59.95   10.347%   $66.153   $66.15   $66.15   $66.20  
  Purchase #2 $59.34   7.768%   $63.9495   $63.95   $63.95   $63.90  
  Purchase #3 $23.82   4.172%   $24.8138   $24.81   $24.80   $24.80  
  Purchase #4 $103.52   13.266%   $117.253   $117.25   $117.25   $117.30  
  Purchase #5 $203.55   7.314%   $218.4376   $218.44   $218.45   $218.40  
  Purchase #6 $61.58   9.460%   $67.4055   $67.41   $67.40   $67.40  
  Purchase #7 $140.82   9.343%   $153.9768   $153.98   $154.00   $154.00  
  7 purchase totals = $652.58       $711.9892   $711.99   $712.00   $712.00