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 $231.25   7.317%   $248.1706   $248.17   $248.15   $248.20  
  Purchase #2 $247.77   5.550%   $261.5212   $261.52   $261.50   $261.50  
  Purchase #3 $78.65   3.408%   $81.3304   $81.33   $81.35   $81.30  
  Purchase #4 $231.28   5.721%   $244.5115   $244.51   $244.50   $244.50  
  Purchase #5 $34.56   5.764%   $36.552   $36.55   $36.55   $36.60  
  Purchase #6 $50.87   8.801%   $55.3471   $55.35   $55.35   $55.30  
  Purchase #7 $212.97   7.757%   $229.4901   $229.49   $229.50   $229.50  
  7 purchase totals = $1,087.35       $1,156.9229   $1,156.92   $1,156.90   $1,156.90