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	$92.36	11.853%	$103.3074	$103.31	$103.30	$103.30
Purchase #2	$77.57	4.306%	$80.9102	$80.91	$80.90	$80.90
Purchase #3	$198.38	8.263%	$214.7721	$214.77	$214.75	$214.80
Purchase #4	$56.55	9.181%	$61.7419	$61.74	$61.75	$61.70
Purchase #5	$88.55	4.342%	$92.3948	$92.39	$92.40	$92.40
Purchase #6	$73.89	11.372%	$82.2928	$82.29	$82.30	$82.30
Purchase #7	$123.94	10.852%	$137.39	$137.39	$137.40	$137.40
7 purchase totals =	$711.24		$772.8092	$772.80	$772.80	$772.80