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 $35.97   7.402%   $38.6325   $38.63   $38.65   $38.60  
  Purchase #2 $223.79   7.275%   $240.0707   $240.07   $240.05   $240.10  
  Purchase #3 $172.54   7.752%   $185.9153   $185.92   $185.90   $185.90  
  Purchase #4 $233.57   7.475%   $251.0294   $251.03   $251.05   $251.00  
  Purchase #5 $25.63   10.821%   $28.4034   $28.40   $28.40   $28.40  
  Purchase #6 $193.81   4.725%   $202.9675   $202.97   $202.95   $203.00  
  Purchase #7 $98.73   5.198%   $103.862   $103.86   $103.85   $103.90  
  7 purchase totals = $984.04       $1,050.8808   $1,050.88   $1,050.85   $1,050.90