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 $78.68   3.814%   $81.6809   $81.68   $81.70   $81.70  
  Purchase #2 $73.58   12.323%   $82.6473   $82.65   $82.65   $82.60  
  Purchase #3 $86.49   9.133%   $94.3891   $94.39   $94.40   $94.40  
  Purchase #4 $225.88   9.397%   $247.1059   $247.11   $247.10   $247.10  
  Purchase #5 $199.56   7.289%   $214.1059   $214.11   $214.10   $214.10  
  Purchase #6 $47.80   9.308%   $52.2492   $52.25   $52.25   $52.20  
  Purchase #7 $73.75   4.343%   $76.953   $76.95   $76.95   $77.00  
  7 purchase totals = $785.74       $849.1313   $849.14   $849.15   $849.10