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 $59.45   11.641%   $66.3706   $66.37   $66.35   $66.40  
  Purchase #2 $244.26   13.711%   $277.7505   $277.75   $277.75   $277.80  
  Purchase #3 $90.88   3.589%   $94.1417   $94.14   $94.15   $94.10  
  Purchase #4 $121.37   8.294%   $131.4364   $131.44   $131.45   $131.40  
  Purchase #5 $48.86   6.126%   $51.8532   $51.85   $51.85   $51.90  
  Purchase #6 $104.76   12.341%   $117.6884   $117.69   $117.70   $117.70  
  Purchase #7 $52.53   9.772%   $57.6632   $57.66   $57.65   $57.70  
  7 purchase totals = $722.11       $796.9040   $796.90   $796.90   $797.00