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 $220.54   5.212%   $232.0345   $232.03   $232.05   $232.00  
  Purchase #2 $247.82   4.476%   $258.9124   $258.91   $258.90   $258.90  
  Purchase #3 $110.87   7.624%   $119.3227   $119.32   $119.30   $119.30  
  Purchase #4 $56.29   12.564%   $63.3623   $63.36   $63.35   $63.40  
  Purchase #5 $118.42   7.759%   $127.6082   $127.61   $127.60   $127.60  
  Purchase #6 $13.64   3.873%   $14.1683   $14.17   $14.15   $14.20  
  Purchase #7 $227.92   4.694%   $238.6186   $238.62   $238.60   $238.60  
  7 purchase totals = $995.50       $1,054.0270   $1,054.02   $1,053.95   $1,054.00