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 $44.32   11.459%   $49.3986   $49.40   $49.40   $49.40  
  Purchase #2 $240.95   10.441%   $266.1076   $266.11   $266.10   $266.10  
  Purchase #3 $73.39   11.397%   $81.7543   $81.75   $81.75   $81.80  
  Purchase #4 $143.56   13.746%   $163.2938   $163.29   $163.30   $163.30  
  Purchase #5 $83.87   5.809%   $88.742   $88.74   $88.75   $88.70  
  Purchase #6 $165.88   13.678%   $188.5691   $188.57   $188.55   $188.60  
  Purchase #7 $214.62   4.370%   $223.9989   $224.00   $224.00   $224.00  
  7 purchase totals = $966.59       $1,061.8643   $1,061.86   $1,061.85   $1,061.90