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 $61.69   10.611%   $68.2359   $68.24   $68.25   $68.20  
  Purchase #2 $176.65   5.766%   $186.8356   $186.84   $186.85   $186.80  
  Purchase #3 $219.89   5.689%   $232.3995   $232.40   $232.40   $232.40  
  Purchase #4 $106.71   4.533%   $111.5472   $111.55   $111.55   $111.50  
  Purchase #5 $223.59   11.789%   $249.949   $249.95   $249.95   $249.90  
  Purchase #6 $231.30   4.593%   $241.9236   $241.92   $241.90   $241.90  
  Purchase #7 $83.63   8.795%   $90.9853   $90.99   $91.00   $91.00  
  7 purchase totals = $1,103.46       $1,181.8761   $1,181.89   $1,181.90   $1,181.70