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 $108.85   13.732%   $123.7973   $123.80   $123.80   $123.80  
  Purchase #2 $177.92   11.242%   $197.9218   $197.92   $197.90   $197.90  
  Purchase #3 $109.37   13.853%   $124.521   $124.52   $124.50   $124.50  
  Purchase #4 $242.26   11.346%   $269.7468   $269.75   $269.75   $269.70  
  Purchase #5 $49.89   9.176%   $54.4679   $54.47   $54.45   $54.50  
  Purchase #6 $224.90   13.395%   $255.0254   $255.03   $255.05   $255.00  
  Purchase #7 $150.69   7.356%   $161.7748   $161.77   $161.75   $161.80  
  7 purchase totals = $1,063.88       $1,187.2550   $1,187.26   $1,187.20   $1,187.20