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 $63.41   11.347%   $70.6051   $70.61   $70.60   $70.60  
  Purchase #2 $95.60   7.124%   $102.4105   $102.41   $102.40   $102.40  
  Purchase #3 $69.43   6.846%   $74.1832   $74.18   $74.20   $74.20  
  Purchase #4 $24.64   5.571%   $26.0127   $26.01   $26.00   $26.00  
  Purchase #5 $107.45   7.747%   $115.7742   $115.77   $115.75   $115.80  
  Purchase #6 $19.88   13.578%   $22.5793   $22.58   $22.60   $22.60  
  Purchase #7 $25.60   10.448%   $28.2747   $28.27   $28.25   $28.30  
  7 purchase totals = $406.01       $439.8397   $439.83   $439.80   $439.90