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 $91.61   9.382%   $100.2049   $100.20   $100.20   $100.20  
  Purchase #2 $232.42   7.114%   $248.9544   $248.95   $248.95   $249.00  
  Purchase #3 $241.43   5.608%   $254.9694   $254.97   $254.95   $255.00  
  Purchase #4 $187.43   3.445%   $193.887   $193.89   $193.90   $193.90  
  Purchase #5 $204.82   4.435%   $213.9038   $213.90   $213.90   $213.90  
  Purchase #6 $54.73   11.841%   $61.2106   $61.21   $61.20   $61.20  
  Purchase #7 $118.31   10.844%   $131.1395   $131.14   $131.15   $131.10  
  7 purchase totals = $1,130.75       $1,204.2696   $1,204.26   $1,204.25   $1,204.30