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 $240.94   8.631%   $261.7355   $261.74   $261.75   $261.70  
  Purchase #2 $223.42   4.600%   $233.6973   $233.70   $233.70   $233.70  
  Purchase #3 $24.80   12.777%   $27.9687   $27.97   $27.95   $28.00  
  Purchase #4 $195.96   8.540%   $212.695   $212.70   $212.70   $212.70  
  Purchase #5 $229.63   10.341%   $253.376   $253.38   $253.40   $253.40  
  Purchase #6 $131.75   7.559%   $141.709   $141.71   $141.70   $141.70  
  Purchase #7 $103.51   9.270%   $113.1054   $113.11   $113.10   $113.10  
  7 purchase totals = $1,150.01       $1,244.2869   $1,244.31   $1,244.30   $1,244.30