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 $212.44   6.832%   $226.9539   $226.95   $226.95   $227.00  
  Purchase #2 $18.42   8.761%   $20.0338   $20.03   $20.05   $20.00  
  Purchase #3 $95.47   11.380%   $106.3345   $106.33   $106.35   $106.30  
  Purchase #4 $172.65   13.243%   $195.514   $195.51   $195.50   $195.50  
  Purchase #5 $59.49   5.849%   $62.9696   $62.97   $62.95   $63.00  
  Purchase #6 $49.72   7.120%   $53.2601   $53.26   $53.25   $53.30  
  Purchase #7 $5.44   10.110%   $5.99   $5.99   $6.00   $6.00  
  7 purchase totals = $613.63       $671.0559   $671.04   $671.05   $671.10