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 $204.61   9.363%   $223.7676   $223.77   $223.75   $223.80  
  Purchase #2 $182.84   12.573%   $205.8285   $205.83   $205.85   $205.80  
  Purchase #3 $26.39   9.580%   $28.9182   $28.92   $28.90   $28.90  
  Purchase #4 $175.53   4.571%   $183.5535   $183.55   $183.55   $183.60  
  Purchase #5 $76.63   12.177%   $85.9612   $85.96   $85.95   $86.00  
  Purchase #6 $158.30   9.854%   $173.8989   $173.90   $173.90   $173.90  
  Purchase #7 $122.60   9.177%   $133.851   $133.85   $133.85   $133.90  
  7 purchase totals = $946.90       $1,035.7789   $1,035.78   $1,035.75   $1,035.90