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 $241.34   9.542%   $264.3687   $264.37   $264.35   $264.40  
  Purchase #2 $240.31   5.349%   $253.1642   $253.16   $253.15   $253.20  
  Purchase #3 $127.31   7.479%   $136.8315   $136.83   $136.85   $136.80  
  Purchase #4 $94.58   4.827%   $99.1454   $99.15   $99.15   $99.10  
  Purchase #5 $5.67   4.214%   $5.9089   $5.91   $5.90   $5.90  
  Purchase #6 $229.72   13.742%   $261.2881   $261.29   $261.30   $261.30  
  Purchase #7 $230.55   7.196%   $247.1404   $247.14   $247.15   $247.10  
  7 purchase totals = $1,169.48       $1,267.8472   $1,267.85   $1,267.85   $1,267.80