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 $86.84   6.229%   $92.2493   $92.25   $92.25   $92.20  
  Purchase #2 $39.82   5.498%   $42.0093   $42.01   $42.00   $42.00  
  Purchase #3 $178.51   4.379%   $186.327   $186.33   $186.35   $186.30  
  Purchase #4 $234.99   5.222%   $247.2612   $247.26   $247.25   $247.30  
  Purchase #5 $162.79   5.806%   $172.2416   $172.24   $172.25   $172.20  
  Purchase #6 $35.39   10.763%   $39.199   $39.20   $39.20   $39.20  
  Purchase #7 $163.62   10.253%   $180.396   $180.40   $180.40   $180.40  
  7 purchase totals = $901.96       $959.6834   $959.69   $959.70   $959.60