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 $72.33   5.116%   $76.0304   $76.03   $76.05   $76.00  
  Purchase #2 $93.53   13.518%   $106.1734   $106.17   $106.15   $106.20  
  Purchase #3 $56.50   11.188%   $62.8212   $62.82   $62.80   $62.80  
  Purchase #4 $18.86   11.104%   $20.9542   $20.95   $20.95   $21.00  
  Purchase #5 $243.32   10.769%   $269.5231   $269.52   $269.50   $269.50  
  Purchase #6 $237.84   11.452%   $265.0774   $265.08   $265.10   $265.10  
  Purchase #7 $168.47   11.708%   $188.1945   $188.19   $188.20   $188.20  
  7 purchase totals = $890.85       $988.7742   $988.76   $988.75   $988.80