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 $214.86   12.532%   $241.7863   $241.79   $241.80   $241.80  
  Purchase #2 $225.57   5.845%   $238.7546   $238.75   $238.75   $238.80  
  Purchase #3 $74.70   3.521%   $77.3302   $77.33   $77.35   $77.30  
  Purchase #4 $235.77   11.392%   $262.6289   $262.63   $262.65   $262.60  
  Purchase #5 $246.82   7.798%   $266.067   $266.07   $266.05   $266.10  
  Purchase #6 $54.38   6.130%   $57.7135   $57.71   $57.70   $57.70  
  Purchase #7 $81.36   4.599%   $85.1017   $85.10   $85.10   $85.10  
  7 purchase totals = $1,133.46       $1,229.3822   $1,229.38   $1,229.40   $1,229.40