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	$114.69	7.437%	$123.2195	$123.22	$123.20	$123.20
Purchase #2	$15.67	11.413%	$17.4584	$17.46	$17.45	$17.50
Purchase #3	$143.53	12.112%	$160.9144	$160.91	$160.90	$160.90
Purchase #4	$171.25	12.340%	$192.3823	$192.38	$192.40	$192.40
Purchase #5	$171.77	4.222%	$179.0221	$179.02	$179.00	$179.00
Purchase #6	$127.31	10.619%	$140.829	$140.83	$140.85	$140.80
Purchase #7	$62.42	11.841%	$69.8112	$69.81	$69.80	$69.80
7 purchase totals =	$806.64		$883.6369	$883.63	$883.60	$883.60