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 $242.61   11.683%   $270.9541   $270.95   $270.95   $271.00  
  Purchase #2 $111.52   9.527%   $122.1445   $122.14   $122.15   $122.10  
  Purchase #3 $215.83   11.197%   $239.9965   $240.00   $240.00   $240.00  
  Purchase #4 $21.61   5.545%   $22.8083   $22.81   $22.80   $22.80  
  Purchase #5 $146.35   4.595%   $153.0748   $153.07   $153.05   $153.10  
  Purchase #6 $171.96   13.120%   $194.5212   $194.52   $194.50   $194.50  
  Purchase #7 $10.39   3.291%   $10.7319   $10.73   $10.75   $10.70  
  7 purchase totals = $920.27       $1,014.2313   $1,014.22   $1,014.20   $1,014.20