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 $129.75   10.695%   $143.6268   $143.63   $143.65   $143.60  
  Purchase #2 $54.30   8.416%   $58.8699   $58.87   $58.85   $58.90  
  Purchase #3 $96.86   12.701%   $109.1622   $109.16   $109.15   $109.20  
  Purchase #4 $178.94   8.225%   $193.6578   $193.66   $193.65   $193.70  
  Purchase #5 $141.42   4.574%   $147.8886   $147.89   $147.90   $147.90  
  Purchase #6 $34.43   13.103%   $38.9414   $38.94   $38.95   $38.90  
  Purchase #7 $64.55   4.251%   $67.294   $67.29   $67.30   $67.30  
  7 purchase totals = $700.25       $759.4407   $759.44   $759.45   $759.50