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 $243.43   7.207%   $260.974   $260.97   $260.95   $261.00  
  Purchase #2 $22.64   3.816%   $23.5039   $23.50   $23.50   $23.50  
  Purchase #3 $11.93   11.363%   $13.2856   $13.29   $13.30   $13.30  
  Purchase #4 $222.78   4.783%   $233.4356   $233.44   $233.45   $233.40  
  Purchase #5 $249.57   11.683%   $278.7273   $278.73   $278.75   $278.70  
  Purchase #6 $19.84   7.747%   $21.377   $21.38   $21.40   $21.40  
  Purchase #7 $204.26   8.448%   $221.5159   $221.52   $221.50   $221.50  
  7 purchase totals = $974.45       $1,052.8193   $1,052.83   $1,052.85   $1,052.80