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 $114.68   4.451%   $119.7844   $119.78   $119.80   $119.80  
  Purchase #2 $177.72   7.587%   $191.2036   $191.20   $191.20   $191.20  
  Purchase #3 $214.26   8.710%   $232.922   $232.92   $232.90   $232.90  
  Purchase #4 $166.86   5.122%   $175.4066   $175.41   $175.40   $175.40  
  Purchase #5 $50.62   6.355%   $53.8369   $53.84   $53.85   $53.80  
  Purchase #6 $87.91   5.804%   $93.0123   $93.01   $93.00   $93.00  
  Purchase #7 $167.29   10.678%   $185.1532   $185.15   $185.15   $185.20  
  7 purchase totals = $979.34       $1,051.3190   $1,051.31   $1,051.30   $1,051.30