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 $181.73   6.178%   $192.9573   $192.96   $192.95   $193.00  
  Purchase #2 $122.54   11.310%   $136.3993   $136.40   $136.40   $136.40  
  Purchase #3 $239.71   10.752%   $265.4836   $265.48   $265.50   $265.50  
  Purchase #4 $73.46   11.363%   $81.8073   $81.81   $81.80   $81.80  
  Purchase #5 $165.63   5.452%   $174.6601   $174.66   $174.65   $174.70  
  Purchase #6 $249.71   13.781%   $284.1225   $284.12   $284.10   $284.10  
  Purchase #7 $43.92   9.555%   $48.1166   $48.12   $48.10   $48.10  
  7 purchase totals = $1,076.70       $1,183.5467   $1,183.55   $1,183.50   $1,183.60