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 $184.63   11.867%   $206.54   $206.54   $206.55   $206.50  
  Purchase #2 $31.65   6.274%   $33.6357   $33.64   $33.65   $33.60  
  Purchase #3 $141.94   9.184%   $154.9758   $154.98   $155.00   $155.00  
  Purchase #4 $170.63   7.277%   $183.0467   $183.05   $183.05   $183.00  
  Purchase #5 $240.91   4.698%   $252.228   $252.23   $252.25   $252.20  
  Purchase #6 $170.94   8.321%   $185.1639   $185.16   $185.15   $185.20  
  Purchase #7 $106.68   13.564%   $121.1501   $121.15   $121.15   $121.20  
  7 purchase totals = $1,047.38       $1,136.7402   $1,136.75   $1,136.80   $1,136.70