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 $183.76   10.147%   $202.4061   $202.41   $202.40   $202.40  
  Purchase #2 $113.47   5.327%   $119.5145   $119.51   $119.50   $119.50  
  Purchase #3 $66.55   3.823%   $69.0942   $69.09   $69.10   $69.10  
  Purchase #4 $102.97   9.490%   $112.7419   $112.74   $112.75   $112.70  
  Purchase #5 $111.94   5.509%   $118.1068   $118.11   $118.10   $118.10  
  Purchase #6 $152.48   12.545%   $171.6086   $171.61   $171.60   $171.60  
  Purchase #7 $212.46   4.626%   $222.2884   $222.29   $222.30   $222.30  
  7 purchase totals = $943.63       $1,015.7605   $1,015.76   $1,015.75   $1,015.70