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 $202.35   11.868%   $226.3649   $226.36   $226.35   $226.40  
  Purchase #2 $144.83   10.259%   $159.6881   $159.69   $159.70   $159.70  
  Purchase #3 $45.76   13.132%   $51.7692   $51.77   $51.75   $51.80  
  Purchase #4 $227.96   11.273%   $253.6579   $253.66   $253.65   $253.70  
  Purchase #5 $223.53   7.319%   $239.8902   $239.89   $239.90   $239.90  
  Purchase #6 $9.67   9.647%   $10.6029   $10.60   $10.60   $10.60  
  Purchase #7 $12.40   10.374%   $13.6864   $13.69   $13.70   $13.70  
  7 purchase totals = $866.50       $955.6596   $955.66   $955.65   $955.80