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 $113.63   7.403%   $122.042   $122.04   $122.05   $122.00  
  Purchase #2 $214.39   4.803%   $224.6872   $224.69   $224.70   $224.70  
  Purchase #3 $18.77   4.490%   $19.6128   $19.61   $19.60   $19.60  
  Purchase #4 $236.86   7.139%   $253.7694   $253.77   $253.75   $253.80  
  Purchase #5 $197.89   12.632%   $222.8875   $222.89   $222.90   $222.90  
  Purchase #6 $47.29   6.821%   $50.5157   $50.52   $50.50   $50.50  
  Purchase #7 $81.75   8.561%   $88.7486   $88.75   $88.75   $88.70  
  7 purchase totals = $910.58       $982.2632   $982.27   $982.25   $982.20