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	$29.26	10.281%	$32.2682	$32.27	$32.25	$32.30
Purchase #2	$52.63	3.590%	$54.5194	$54.52	$54.50	$54.50
Purchase #3	$184.83	7.620%	$198.914	$198.91	$198.90	$198.90
Purchase #4	$98.61	10.732%	$109.1928	$109.19	$109.20	$109.20
Purchase #5	$184.69	4.332%	$192.6908	$192.69	$192.70	$192.70
Purchase #6	$14.72	7.483%	$15.8215	$15.82	$15.80	$15.80
Purchase #7	$54.93	13.689%	$62.4494	$62.45	$62.45	$62.40
7 purchase totals =	$619.67		$665.8561	$665.85	$665.80	$665.80