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 $222.86   11.654%   $248.8321   $248.83   $248.85   $248.80  
  Purchase #2 $58.72   13.868%   $66.8633   $66.86   $66.85   $66.90  
  Purchase #3 $99.32   13.472%   $112.7004   $112.70   $112.70   $112.70  
  Purchase #4 $91.81   6.823%   $98.0742   $98.07   $98.05   $98.10  
  Purchase #5 $201.98   6.816%   $215.747   $215.75   $215.75   $215.70  
  Purchase #6 $84.81   12.589%   $95.4867   $95.49   $95.50   $95.50  
  Purchase #7 $131.77   7.511%   $141.6672   $141.67   $141.65   $141.70  
  7 purchase totals = $891.27       $979.3709   $979.37   $979.35   $979.40