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 $246.89   8.287%   $267.3498   $267.35   $267.35   $267.30  
  Purchase #2 $205.87   4.809%   $215.7703   $215.77   $215.75   $215.80  
  Purchase #3 $169.55   5.615%   $179.0702   $179.07   $179.05   $179.10  
  Purchase #4 $34.90   7.141%   $37.3922   $37.39   $37.40   $37.40  
  Purchase #5 $86.86   12.377%   $97.6107   $97.61   $97.60   $97.60  
  Purchase #6 $80.65   11.599%   $90.0046   $90.00   $90.00   $90.00  
  Purchase #7 $163.45   7.835%   $176.2563   $176.26   $176.25   $176.30  
  7 purchase totals = $988.17       $1,063.4541   $1,063.45   $1,063.40   $1,063.50