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	$21.91	6.439%	$23.3208	$23.32	$23.30	$23.30
Purchase #2	$245.63	12.336%	$275.9309	$275.93	$275.95	$275.90
Purchase #3	$88.25	9.424%	$96.5667	$96.57	$96.55	$96.60
Purchase #4	$143.76	6.753%	$153.4681	$153.47	$153.45	$153.50
Purchase #5	$215.45	6.222%	$228.8553	$228.86	$228.85	$228.90
Purchase #6	$40.89	6.768%	$43.6574	$43.66	$43.65	$43.70
Purchase #7	$97.38	8.181%	$105.3467	$105.35	$105.35	$105.30
7 purchase totals =	$853.27		$927.1459	$927.16	$927.10	$927.20