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 $244.53   10.261%   $269.6212   $269.62   $269.60   $269.60  
  Purchase #2 $90.78   9.674%   $99.5621   $99.56   $99.55   $99.60  
  Purchase #3 $225.76   9.271%   $246.6902   $246.69   $246.70   $246.70  
  Purchase #4 $23.76   12.343%   $26.6927   $26.69   $26.70   $26.70  
  Purchase #5 $224.44   6.817%   $239.7401   $239.74   $239.75   $239.70  
  Purchase #6 $169.45   3.171%   $174.8233   $174.82   $174.80   $174.80  
  Purchase #7 $63.66   3.178%   $65.6831   $65.68   $65.70   $65.70  
  7 purchase totals = $1,042.38       $1,122.8127   $1,122.80   $1,122.80   $1,122.80