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 $73.61   11.437%   $82.0288   $82.03   $82.05   $82.00  
  Purchase #2 $23.46   4.788%   $24.5833   $24.58   $24.60   $24.60  
  Purchase #3 $54.94   11.154%   $61.068   $61.07   $61.05   $61.10  
  Purchase #4 $58.77   5.496%   $62   $62.00   $62.00   $62.00  
  Purchase #5 $103.66   12.829%   $116.9585   $116.96   $116.95   $117.00  
  Purchase #6 $44.39   6.828%   $47.4209   $47.42   $47.40   $47.40  
  Purchase #7 $27.99   5.510%   $29.5322   $29.53   $29.55   $29.50  
  7 purchase totals = $386.82       $423.5917   $423.59   $423.60   $423.60