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 $181.32   12.857%   $204.6323   $204.63   $204.65   $204.60  
  Purchase #2 $230.96   4.744%   $241.9167   $241.92   $241.90   $241.90  
  Purchase #3 $53.90   3.111%   $55.5768   $55.58   $55.60   $55.60  
  Purchase #4 $181.79   7.180%   $194.8425   $194.84   $194.85   $194.80  
  Purchase #5 $213.89   13.217%   $242.1598   $242.16   $242.15   $242.20  
  Purchase #6 $178.95   12.410%   $201.1577   $201.16   $201.15   $201.20  
  Purchase #7 $175.34   12.858%   $197.8852   $197.89   $197.90   $197.90  
  7 purchase totals = $1,216.15       $1,338.1710   $1,338.18   $1,338.20   $1,338.20