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 $79.59   4.611%   $83.2599   $83.26   $83.25   $83.30  
  Purchase #2 $229.69   9.864%   $252.3466   $252.35   $252.35   $252.30  
  Purchase #3 $246.88   5.766%   $261.1151   $261.12   $261.10   $261.10  
  Purchase #4 $94.90   12.365%   $106.6344   $106.63   $106.65   $106.60  
  Purchase #5 $158.59   5.665%   $167.5741   $167.57   $167.55   $167.60  
  Purchase #6 $189.43   6.288%   $201.3414   $201.34   $201.35   $201.30  
  Purchase #7 $176.31   11.128%   $195.9298   $195.93   $195.95   $195.90  
  7 purchase totals = $1,175.39       $1,268.2013   $1,268.20   $1,268.20   $1,268.10