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 $61.29   11.826%   $68.5382   $68.54   $68.55   $68.50  
  Purchase #2 $46.64   3.825%   $48.424   $48.42   $48.40   $48.40  
  Purchase #3 $168.82   11.721%   $188.6074   $188.61   $188.60   $188.60  
  Purchase #4 $55.25   6.491%   $58.8363   $58.84   $58.85   $58.80  
  Purchase #5 $93.35   5.554%   $98.5347   $98.53   $98.55   $98.50  
  Purchase #6 $152.40   6.317%   $162.0271   $162.03   $162.05   $162.00  
  Purchase #7 $226.47   8.634%   $246.0234   $246.02   $246.00   $246.00  
  7 purchase totals = $804.22       $870.9911   $870.99   $871.00   $870.80