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 $141.36   7.288%   $151.6623   $151.66   $151.65   $151.70  
  Purchase #2 $186.74   11.203%   $207.6605   $207.66   $207.65   $207.70  
  Purchase #3 $73.53   3.404%   $76.033   $76.03   $76.05   $76.00  
  Purchase #4 $227.26   6.113%   $241.1524   $241.15   $241.15   $241.20  
  Purchase #5 $83.62   6.456%   $89.0185   $89.02   $89.00   $89.00  
  Purchase #6 $184.26   11.208%   $204.9119   $204.91   $204.90   $204.90  
  Purchase #7 $8.84   5.518%   $9.3278   $9.33   $9.35   $9.30  
  7 purchase totals = $905.61       $979.7664   $979.76   $979.75   $979.80