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 $119.27   8.285%   $129.1515   $129.15   $129.15   $129.20  
  Purchase #2 $76.89   11.837%   $85.9915   $85.99   $86.00   $86.00  
  Purchase #3 $84.40   13.811%   $96.0565   $96.06   $96.05   $96.10  
  Purchase #4 $250.55   7.640%   $269.692   $269.69   $269.70   $269.70  
  Purchase #5 $98.33   11.472%   $109.6104   $109.61   $109.60   $109.60  
  Purchase #6 $24.99   4.162%   $26.0301   $26.03   $26.05   $26.00  
  Purchase #7 $14.68   10.287%   $16.1901   $16.19   $16.20   $16.20  
  7 purchase totals = $669.11       $732.7221   $732.72   $732.75   $732.80