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 $64.79   6.509%   $69.0072   $69.01   $69.00   $69.00  
  Purchase #2 $100.74   6.426%   $107.2136   $107.21   $107.20   $107.20  
  Purchase #3 $137.66   6.727%   $146.9204   $146.92   $146.90   $146.90  
  Purchase #4 $29.87   12.815%   $33.6978   $33.70   $33.70   $33.70  
  Purchase #5 $31.80   13.624%   $36.1324   $36.13   $36.15   $36.10  
  Purchase #6 $137.62   5.721%   $145.4932   $145.49   $145.50   $145.50  
  Purchase #7 $21.89   12.344%   $24.5921   $24.59   $24.60   $24.60  
  7 purchase totals = $524.37       $563.0567   $563.05   $563.05   $563.00