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 $55.36   3.567%   $57.3347   $57.33   $57.35   $57.30  
  Purchase #2 $8.92   8.505%   $9.6786   $9.68   $9.70   $9.70  
  Purchase #3 $93.68   3.721%   $97.1658   $97.17   $97.15   $97.20  
  Purchase #4 $247.78   5.447%   $261.2766   $261.28   $261.30   $261.30  
  Purchase #5 $23.52   8.246%   $25.4595   $25.46   $25.45   $25.50  
  Purchase #6 $15.57   12.505%   $17.517   $17.52   $17.50   $17.50  
  Purchase #7 $220.75   5.790%   $233.5314   $233.53   $233.55   $233.50  
  7 purchase totals = $665.58       $701.9636   $701.97   $702.00   $702.00