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 $244.59   10.193%   $269.5211   $269.52   $269.50   $269.50  
  Purchase #2 $82.55   13.347%   $93.5679   $93.57   $93.55   $93.60  
  Purchase #3 $60.71   7.171%   $65.0635   $65.06   $65.05   $65.10  
  Purchase #4 $117.41   6.627%   $125.1908   $125.19   $125.20   $125.20  
  Purchase #5 $42.96   6.676%   $45.828   $45.83   $45.85   $45.80  
  Purchase #6 $42.97   13.589%   $48.8092   $48.81   $48.80   $48.80  
  Purchase #7 $33.30   4.228%   $34.7079   $34.71   $34.70   $34.70  
  7 purchase totals = $624.49       $682.6884   $682.69   $682.65   $682.70