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 $41.81   3.323%   $43.1993   $43.20   $43.20   $43.20  
  Purchase #2 $196.81   8.393%   $213.3283   $213.33   $213.35   $213.30  
  Purchase #3 $229.90   5.643%   $242.8733   $242.87   $242.85   $242.90  
  Purchase #4 $211.95   10.417%   $234.0288   $234.03   $234.05   $234.00  
  Purchase #5 $185.93   13.763%   $211.5195   $211.52   $211.50   $211.50  
  Purchase #6 $183.72   4.560%   $192.0976   $192.10   $192.10   $192.10  
  Purchase #7 $136.42   5.170%   $143.4729   $143.47   $143.45   $143.50  
  7 purchase totals = $1,186.54       $1,280.5197   $1,280.52   $1,280.50   $1,280.50