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 $69.64   9.347%   $76.1493   $76.15   $76.15   $76.10  
  Purchase #2 $61.80   6.229%   $65.6495   $65.65   $65.65   $65.60  
  Purchase #3 $244.32   6.325%   $259.7732   $259.77   $259.75   $259.80  
  Purchase #4 $90.67   8.314%   $98.2083   $98.21   $98.20   $98.20  
  Purchase #5 $167.60   7.452%   $180.0896   $180.09   $180.10   $180.10  
  Purchase #6 $11.25   10.184%   $12.3957   $12.40   $12.40   $12.40  
  Purchase #7 $235.66   5.688%   $249.0643   $249.06   $249.05   $249.10  
  7 purchase totals = $880.94       $941.3299   $941.33   $941.30   $941.30