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 $232.63   8.643%   $252.7362   $252.74   $252.75   $252.70  
  Purchase #2 $188.38   8.491%   $204.3753   $204.38   $204.40   $204.40  
  Purchase #3 $194.47   10.422%   $214.7377   $214.74   $214.75   $214.70  
  Purchase #4 $48.89   8.347%   $52.9708   $52.97   $52.95   $53.00  
  Purchase #5 $236.51   11.199%   $262.9968   $263.00   $263.00   $263.00  
  Purchase #6 $73.53   7.177%   $78.8072   $78.81   $78.80   $78.80  
  Purchase #7 $7.79   9.514%   $8.5311   $8.53   $8.55   $8.50  
  7 purchase totals = $982.20       $1,075.1551   $1,075.17   $1,075.20   $1,075.10