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 $232.48   11.787%   $259.8824   $259.88   $259.90   $259.90  
  Purchase #2 $167.39   7.298%   $179.6061   $179.61   $179.60   $179.60  
  Purchase #3 $176.38   8.517%   $191.4023   $191.40   $191.40   $191.40  
  Purchase #4 $65.34   4.500%   $68.2803   $68.28   $68.30   $68.30  
  Purchase #5 $27.73   3.831%   $28.7923   $28.79   $28.80   $28.80  
  Purchase #6 $116.49   11.839%   $130.2813   $130.28   $130.30   $130.30  
  Purchase #7 $183.78   11.577%   $205.0562   $205.06   $205.05   $205.10  
  7 purchase totals = $969.59       $1,063.3009   $1,063.30   $1,063.35   $1,063.40