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 $67.57   7.680%   $72.7594   $72.76   $72.75   $72.80  
  Purchase #2 $57.25   13.845%   $65.1763   $65.18   $65.20   $65.20  
  Purchase #3 $56.32   4.681%   $58.9563   $58.96   $58.95   $59.00  
  Purchase #4 $191.84   10.501%   $211.9851   $211.99   $212.00   $212.00  
  Purchase #5 $82.79   9.140%   $90.357   $90.36   $90.35   $90.40  
  Purchase #6 $229.85   5.340%   $242.124   $242.12   $242.10   $242.10  
  Purchase #7 $8.43   3.125%   $8.6934   $8.69   $8.70   $8.70  
  7 purchase totals = $694.05       $750.0515   $750.06   $750.05   $750.20