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 $247.54   8.664%   $268.9869   $268.99   $269.00   $269.00  
  Purchase #2 $238.74   5.270%   $251.3216   $251.32   $251.30   $251.30  
  Purchase #3 $209.55   9.844%   $230.1781   $230.18   $230.20   $230.20  
  Purchase #4 $15.83   6.633%   $16.88   $16.88   $16.90   $16.90  
  Purchase #5 $156.45   6.119%   $166.0232   $166.02   $166.00   $166.00  
  Purchase #6 $188.70   4.419%   $197.0387   $197.04   $197.05   $197.00  
  Purchase #7 $205.73   7.611%   $221.3881   $221.39   $221.40   $221.40  
  7 purchase totals = $1,262.54       $1,351.8166   $1,351.82   $1,351.85   $1,351.80