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 $209.98   12.178%   $235.5514   $235.55   $235.55   $235.60  
  Purchase #2 $104.95   6.397%   $111.6637   $111.66   $111.65   $111.70  
  Purchase #3 $151.36   9.432%   $165.6363   $165.64   $165.65   $165.60  
  Purchase #4 $101.34   3.593%   $104.9811   $104.98   $105.00   $105.00  
  Purchase #5 $136.30   13.119%   $154.1812   $154.18   $154.20   $154.20  
  Purchase #6 $90.86   9.214%   $99.2318   $99.23   $99.25   $99.20  
  Purchase #7 $208.69   12.608%   $235.0016   $235.00   $235.00   $235.00  
  7 purchase totals = $1,003.48       $1,106.2471   $1,106.24   $1,106.30   $1,106.30