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 $111.43   13.113%   $126.0418   $126.04   $126.05   $126.00  
  Purchase #2 $151.53   10.162%   $166.9285   $166.93   $166.95   $166.90  
  Purchase #3 $60.91   6.599%   $64.9295   $64.93   $64.95   $64.90  
  Purchase #4 $226.59   10.778%   $251.0119   $251.01   $251.00   $251.00  
  Purchase #5 $151.37   4.794%   $158.6267   $158.63   $158.65   $158.60  
  Purchase #6 $146.95   13.806%   $167.2379   $167.24   $167.25   $167.20  
  Purchase #7 $92.52   7.151%   $99.1361   $99.14   $99.15   $99.10  
  7 purchase totals = $941.30       $1,033.9124   $1,033.92   $1,034.00   $1,033.70