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 $80.82   6.787%   $86.3053   $86.31   $86.30   $86.30  
  Purchase #2 $235.76   13.659%   $267.9625   $267.96   $267.95   $268.00  
  Purchase #3 $35.57   8.737%   $38.6778   $38.68   $38.70   $38.70  
  Purchase #4 $8.91   6.848%   $9.5202   $9.52   $9.50   $9.50  
  Purchase #5 $96.49   13.461%   $109.4785   $109.48   $109.50   $109.50  
  Purchase #6 $142.34   8.125%   $153.9051   $153.91   $153.90   $153.90  
  Purchase #7 $32.64   4.600%   $34.1414   $34.14   $34.15   $34.10  
  7 purchase totals = $632.53       $699.9908   $700.00   $700.00   $700.00