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 $61.97   8.234%   $67.0726   $67.07   $67.05   $67.10  
  Purchase #2 $186.72   6.673%   $199.1798   $199.18   $199.20   $199.20  
  Purchase #3 $198.98   12.693%   $224.2365   $224.24   $224.25   $224.20  
  Purchase #4 $173.82   11.490%   $193.7919   $193.79   $193.80   $193.80  
  Purchase #5 $179.69   11.196%   $199.8081   $199.81   $199.80   $199.80  
  Purchase #6 $26.86   4.579%   $28.0899   $28.09   $28.10   $28.10  
  Purchase #7 $103.89   12.143%   $116.5054   $116.51   $116.50   $116.50  
  7 purchase totals = $931.93       $1,028.6842   $1,028.69   $1,028.70   $1,028.70