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 $86.60   8.211%   $93.7107   $93.71   $93.70   $93.70  
  Purchase #2 $216.98   11.185%   $241.2492   $241.25   $241.25   $241.20  
  Purchase #3 $44.51   5.269%   $46.8552   $46.86   $46.85   $46.90  
  Purchase #4 $244.30   8.583%   $265.2683   $265.27   $265.25   $265.30  
  Purchase #5 $55.67   7.769%   $59.995   $60.00   $60.00   $60.00  
  Purchase #6 $119.44   4.666%   $125.0131   $125.01   $125.00   $125.00  
  Purchase #7 $176.57   6.125%   $187.3849   $187.38   $187.40   $187.40  
  7 purchase totals = $944.07       $1,019.4764   $1,019.48   $1,019.45   $1,019.50