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 $86.67   8.183%   $93.7622   $93.76   $93.75   $93.80  
  Purchase #2 $209.30   4.712%   $219.1622   $219.16   $219.15   $219.20  
  Purchase #3 $115.60   13.454%   $131.1528   $131.15   $131.15   $131.20  
  Purchase #4 $99.36   4.159%   $103.4924   $103.49   $103.50   $103.50  
  Purchase #5 $175.65   13.239%   $198.9043   $198.90   $198.90   $198.90  
  Purchase #6 $22.37   4.174%   $23.3037   $23.30   $23.30   $23.30  
  Purchase #7 $12.46   13.585%   $14.1527   $14.15   $14.15   $14.20  
  7 purchase totals = $721.41       $783.9303   $783.91   $783.90   $784.10