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 $168.71   13.217%   $191.0084   $191.01   $191.00   $191.00  
  Purchase #2 $237.55   3.563%   $246.0139   $246.01   $246.00   $246.00  
  Purchase #3 $109.58   5.610%   $115.7274   $115.73   $115.75   $115.70  
  Purchase #4 $180.90   13.247%   $204.8638   $204.86   $204.85   $204.90  
  Purchase #5 $183.99   6.858%   $196.608   $196.61   $196.60   $196.60  
  Purchase #6 $216.33   11.224%   $240.6109   $240.61   $240.60   $240.60  
  Purchase #7 $92.33   6.848%   $98.6528   $98.65   $98.65   $98.70  
  7 purchase totals = $1,189.39       $1,293.4852   $1,293.48   $1,293.45   $1,293.50