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 $58.58   4.834%   $61.4118   $61.41   $61.40   $61.40  
  Purchase #2 $31.88   5.268%   $33.5594   $33.56   $33.55   $33.60  
  Purchase #3 $95.35   6.679%   $101.7184   $101.72   $101.70   $101.70  
  Purchase #4 $25.89   3.685%   $26.844   $26.84   $26.85   $26.80  
  Purchase #5 $202.52   6.593%   $215.8721   $215.87   $215.85   $215.90  
  Purchase #6 $45.53   5.548%   $48.056   $48.06   $48.05   $48.10  
  Purchase #7 $96.77   4.465%   $101.0908   $101.09   $101.10   $101.10  
  7 purchase totals = $556.52       $588.5525   $588.55   $588.50   $588.60