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 $52.76   11.852%   $59.0131   $59.01   $59.00   $59.00  
  Purchase #2 $56.43   6.504%   $60.1002   $60.10   $60.10   $60.10  
  Purchase #3 $78.64   10.560%   $86.9444   $86.94   $86.95   $86.90  
  Purchase #4 $92.82   5.541%   $97.9632   $97.96   $97.95   $98.00  
  Purchase #5 $210.68   9.618%   $230.9432   $230.94   $230.95   $230.90  
  Purchase #6 $113.92   10.799%   $126.2222   $126.22   $126.20   $126.20  
  Purchase #7 $90.84   13.286%   $102.909   $102.91   $102.90   $102.90  
  7 purchase totals = $696.09       $764.0953   $764.08   $764.05   $764.00