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 $138.79   9.145%   $151.4823   $151.48   $151.50   $151.50  
  Purchase #2 $53.62   8.488%   $58.1713   $58.17   $58.15   $58.20  
  Purchase #3 $178.63   11.228%   $198.6866   $198.69   $198.70   $198.70  
  Purchase #4 $214.26   4.420%   $223.7303   $223.73   $223.75   $223.70  
  Purchase #5 $159.70   6.267%   $169.7084   $169.71   $169.70   $169.70  
  Purchase #6 $163.66   12.531%   $184.1682   $184.17   $184.15   $184.20  
  Purchase #7 $117.65   12.394%   $132.2315   $132.23   $132.25   $132.20  
  7 purchase totals = $1,026.31       $1,118.1786   $1,118.18   $1,118.20   $1,118.20