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 $68.44   7.363%   $73.4792   $73.48   $73.50   $73.50  
  Purchase #2 $223.57   4.250%   $233.0717   $233.07   $233.05   $233.10  
  Purchase #3 $19.60   9.778%   $21.5165   $21.52   $21.50   $21.50  
  Purchase #4 $237.38   12.422%   $266.8673   $266.87   $266.85   $266.90  
  Purchase #5 $178.29   7.469%   $191.6065   $191.61   $191.60   $191.60  
  Purchase #6 $48.74   4.328%   $50.8495   $50.85   $50.85   $50.80  
  Purchase #7 $219.95   5.665%   $232.4102   $232.41   $232.40   $232.40  
  7 purchase totals = $995.97       $1,069.8009   $1,069.81   $1,069.75   $1,069.80