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 $249.71   4.583%   $261.1542   $261.15   $261.15   $261.20  
  Purchase #2 $150.71   11.333%   $167.79   $167.79   $167.80   $167.80  
  Purchase #3 $17.49   13.480%   $19.8477   $19.85   $19.85   $19.80  
  Purchase #4 $247.43   3.713%   $256.6171   $256.62   $256.60   $256.60  
  Purchase #5 $213.39   12.565%   $240.2025   $240.20   $240.20   $240.20  
  Purchase #6 $153.91   12.417%   $173.021   $173.02   $173.00   $173.00  
  Purchase #7 $113.72   12.803%   $128.2796   $128.28   $128.30   $128.30  
  7 purchase totals = $1,146.36       $1,246.9121   $1,246.91   $1,246.90   $1,246.90