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 $56.86   12.526%   $63.9823   $63.98   $64.00   $64.00  
  Purchase #2 $74.28   13.369%   $84.2105   $84.21   $84.20   $84.20  
  Purchase #3 $197.46   8.422%   $214.0901   $214.09   $214.10   $214.10  
  Purchase #4 $88.54   7.626%   $95.2921   $95.29   $95.30   $95.30  
  Purchase #5 $104.72   4.666%   $109.6062   $109.61   $109.60   $109.60  
  Purchase #6 $109.80   5.286%   $115.604   $115.60   $115.60   $115.60  
  Purchase #7 $88.40   4.588%   $92.4558   $92.46   $92.45   $92.50  
  7 purchase totals = $720.06       $775.2410   $775.24   $775.25   $775.30