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 $233.34   8.122%   $252.2919   $252.29   $252.30   $252.30  
  Purchase #2 $15.61   8.342%   $16.9122   $16.91   $16.90   $16.90  
  Purchase #3 $43.75   8.806%   $47.6026   $47.60   $47.60   $47.60  
  Purchase #4 $44.78   11.807%   $50.0672   $50.07   $50.05   $50.10  
  Purchase #5 $194.91   11.842%   $217.9912   $217.99   $218.00   $218.00  
  Purchase #6 $200.85   6.603%   $214.1121   $214.11   $214.10   $214.10  
  Purchase #7 $222.59   7.519%   $239.3265   $239.33   $239.35   $239.30  
  7 purchase totals = $955.83       $1,038.3037   $1,038.30   $1,038.30   $1,038.30