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 $57.52   7.664%   $61.9283   $61.93   $61.95   $61.90  
  Purchase #2 $24.52   5.412%   $25.847   $25.85   $25.85   $25.80  
  Purchase #3 $143.73   6.267%   $152.7376   $152.74   $152.75   $152.70  
  Purchase #4 $30.89   10.524%   $34.1409   $34.14   $34.15   $34.10  
  Purchase #5 $106.72   10.209%   $117.615   $117.62   $117.60   $117.60  
  Purchase #6 $100.85   13.258%   $114.2207   $114.22   $114.20   $114.20  
  Purchase #7 $232.89   5.858%   $246.5327   $246.53   $246.55   $246.50  
  7 purchase totals = $697.12       $753.0222   $753.03   $753.05   $752.80