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 $249.89   3.720%   $259.1859   $259.19   $259.20   $259.20  
  Purchase #2 $219.81   3.671%   $227.8792   $227.88   $227.90   $227.90  
  Purchase #3 $102.40   12.571%   $115.2727   $115.27   $115.25   $115.30  
  Purchase #4 $180.63   6.147%   $191.7333   $191.73   $191.75   $191.70  
  Purchase #5 $211.95   12.231%   $237.8736   $237.87   $237.85   $237.90  
  Purchase #6 $57.65   13.102%   $65.2033   $65.20   $65.20   $65.20  
  Purchase #7 $147.52   10.354%   $162.7942   $162.79   $162.80   $162.80  
  7 purchase totals = $1,169.85       $1,259.9422   $1,259.93   $1,259.95   $1,260.00