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 $218.64   6.195%   $232.1847   $232.18   $232.20   $232.20  
  Purchase #2 $101.77   11.454%   $113.4267   $113.43   $113.45   $113.40  
  Purchase #3 $174.37   5.136%   $183.3256   $183.33   $183.35   $183.30  
  Purchase #4 $142.40   4.107%   $148.2484   $148.25   $148.25   $148.20  
  Purchase #5 $199.29   6.579%   $212.4013   $212.40   $212.40   $212.40  
  Purchase #6 $249.47   8.682%   $271.129   $271.13   $271.15   $271.10  
  Purchase #7 $101.30   5.246%   $106.6142   $106.61   $106.60   $106.60  
  7 purchase totals = $1,187.24       $1,267.3299   $1,267.33   $1,267.40   $1,267.20