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 $58.57   8.737%   $63.6873   $63.69   $63.70   $63.70  
  Purchase #2 $230.38   5.259%   $242.4957   $242.50   $242.50   $242.50  
  Purchase #3 $167.67   13.849%   $190.8906   $190.89   $190.90   $190.90  
  Purchase #4 $51.64   11.873%   $57.7712   $57.77   $57.75   $57.80  
  Purchase #5 $175.47   10.856%   $194.519   $194.52   $194.50   $194.50  
  Purchase #6 $164.37   7.597%   $176.8572   $176.86   $176.85   $176.90  
  Purchase #7 $96.88   7.844%   $104.4793   $104.48   $104.50   $104.50  
  7 purchase totals = $944.98       $1,030.7003   $1,030.71   $1,030.70   $1,030.80