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 $234.86   9.642%   $257.5052   $257.51   $257.50   $257.50  
  Purchase #2 $221.90   9.469%   $242.9117   $242.91   $242.90   $242.90  
  Purchase #3 $114.53   10.778%   $126.874   $126.87   $126.85   $126.90  
  Purchase #4 $21.99   13.349%   $24.9254   $24.93   $24.95   $24.90  
  Purchase #5 $203.68   9.140%   $222.2964   $222.30   $222.30   $222.30  
  Purchase #6 $22.34   10.649%   $24.719   $24.72   $24.70   $24.70  
  Purchase #7 $118.59   3.640%   $122.9067   $122.91   $122.90   $122.90  
  7 purchase totals = $937.89       $1,022.1384   $1,022.15   $1,022.10   $1,022.10