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 $61.25   12.196%   $68.7201   $68.72   $68.70   $68.70  
  Purchase #2 $229.87   13.767%   $261.5162   $261.52   $261.50   $261.50  
  Purchase #3 $135.95   12.341%   $152.7276   $152.73   $152.75   $152.70  
  Purchase #4 $229.74   10.424%   $253.6881   $253.69   $253.70   $253.70  
  Purchase #5 $142.77   3.724%   $148.0868   $148.09   $148.10   $148.10  
  Purchase #6 $237.53   3.713%   $246.3495   $246.35   $246.35   $246.30  
  Purchase #7 $72.70   4.276%   $75.8087   $75.81   $75.80   $75.80  
  7 purchase totals = $1,109.81       $1,206.8970   $1,206.91   $1,206.90   $1,206.80