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 $184.62   11.387%   $205.6427   $205.64   $205.65   $205.60  
  Purchase #2 $16.33   6.795%   $17.4396   $17.44   $17.45   $17.40  
  Purchase #3 $68.98   10.388%   $76.1456   $76.15   $76.15   $76.10  
  Purchase #4 $29.78   6.617%   $31.7505   $31.75   $31.75   $31.80  
  Purchase #5 $163.83   4.605%   $171.3744   $171.37   $171.35   $171.40  
  Purchase #6 $118.42   7.178%   $126.9202   $126.92   $126.90   $126.90  
  Purchase #7 $229.41   6.617%   $244.5901   $244.59   $244.60   $244.60  
  7 purchase totals = $811.37       $873.8631   $873.86   $873.85   $873.80