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 $185.32   8.806%   $201.6393   $201.64   $201.65   $201.60  
  Purchase #2 $124.64   8.570%   $135.3216   $135.32   $135.30   $135.30  
  Purchase #3 $163.89   8.181%   $177.2978   $177.30   $177.30   $177.30  
  Purchase #4 $109.31   3.129%   $112.7303   $112.73   $112.75   $112.70  
  Purchase #5 $143.88   3.267%   $148.5806   $148.58   $148.60   $148.60  
  Purchase #6 $222.53   12.304%   $249.9101   $249.91   $249.90   $249.90  
  Purchase #7 $111.34   13.842%   $126.7517   $126.75   $126.75   $126.80  
  7 purchase totals = $1,060.91       $1,152.2314   $1,152.23   $1,152.25   $1,152.20