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 $151.97   10.210%   $167.4861   $167.49   $167.50   $167.50  
  Purchase #2 $239.59   13.662%   $272.3228   $272.32   $272.30   $272.30  
  Purchase #3 $165.45   8.845%   $180.0841   $180.08   $180.10   $180.10  
  Purchase #4 $197.95   4.554%   $206.9646   $206.96   $206.95   $207.00  
  Purchase #5 $167.75   10.477%   $185.3252   $185.33   $185.35   $185.30  
  Purchase #6 $101.62   4.638%   $106.3331   $106.33   $106.35   $106.30  
  Purchase #7 $66.76   13.859%   $76.0123   $76.01   $76.00   $76.00  
  7 purchase totals = $1,091.09       $1,194.5282   $1,194.52   $1,194.55   $1,194.50