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 $82.73   13.287%   $93.7223   $93.72   $93.70   $93.70  
  Purchase #2 $220.78   13.778%   $251.1991   $251.20   $251.20   $251.20  
  Purchase #3 $55.49   9.615%   $60.8254   $60.83   $60.85   $60.80  
  Purchase #4 $168.44   11.230%   $187.3558   $187.36   $187.35   $187.40  
  Purchase #5 $21.64   8.681%   $23.5186   $23.52   $23.50   $23.50  
  Purchase #6 $67.46   9.499%   $73.868   $73.87   $73.85   $73.90  
  Purchase #7 $108.57   5.444%   $114.4806   $114.48   $114.50   $114.50  
  7 purchase totals = $725.11       $804.9698   $804.98   $804.95   $805.00