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 $218.39   8.332%   $236.5863   $236.59   $236.60   $236.60  
  Purchase #2 $117.30   12.586%   $132.0634   $132.06   $132.05   $132.10  
  Purchase #3 $53.37   12.182%   $59.8715   $59.87   $59.85   $59.90  
  Purchase #4 $168.78   4.572%   $176.4966   $176.50   $176.50   $176.50  
  Purchase #5 $6.61   5.774%   $6.9917   $6.99   $7.00   $7.00  
  Purchase #6 $115.90   7.220%   $124.268   $124.27   $124.25   $124.30  
  Purchase #7 $181.90   8.521%   $197.3997   $197.40   $197.40   $197.40  
  7 purchase totals = $862.25       $933.6772   $933.68   $933.65   $933.80