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 $230.98   4.351%   $241.0299   $241.03   $241.05   $241.00  
  Purchase #2 $108.61   12.131%   $121.7855   $121.79   $121.80   $121.80  
  Purchase #3 $171.46   5.119%   $180.237   $180.24   $180.25   $180.20  
  Purchase #4 $147.25   7.641%   $158.5014   $158.50   $158.50   $158.50  
  Purchase #5 $12.89   7.473%   $13.8533   $13.85   $13.85   $13.90  
  Purchase #6 $125.77   12.688%   $141.7277   $141.73   $141.75   $141.70  
  Purchase #7 $156.47   5.762%   $165.4858   $165.49   $165.50   $165.50  
  7 purchase totals = $953.43       $1,022.6206   $1,022.63   $1,022.70   $1,022.60