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 $68.94   4.156%   $71.8051   $71.81   $71.80   $71.80  
  Purchase #2 $99.56   8.186%   $107.71   $107.71   $107.70   $107.70  
  Purchase #3 $19.85   12.431%   $22.3176   $22.32   $22.30   $22.30  
  Purchase #4 $173.76   6.459%   $184.9832   $184.98   $185.00   $185.00  
  Purchase #5 $218.42   12.287%   $245.2573   $245.26   $245.25   $245.30  
  Purchase #6 $184.91   6.243%   $196.4539   $196.45   $196.45   $196.50  
  Purchase #7 $16.63   3.874%   $17.2742   $17.27   $17.25   $17.30  
  7 purchase totals = $782.07       $845.8013   $845.80   $845.75   $845.90