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	$25.84	11.727%	$28.8703	$28.87	$28.85	$28.90
Purchase #2	$198.56	7.119%	$212.6955	$212.70	$212.70	$212.70
Purchase #3	$61.27	7.594%	$65.9228	$65.92	$65.90	$65.90
Purchase #4	$151.77	8.597%	$164.8177	$164.82	$164.80	$164.80
Purchase #5	$153.63	13.357%	$174.1504	$174.15	$174.15	$174.20
Purchase #6	$33.30	11.476%	$37.1215	$37.12	$37.10	$37.10
Purchase #7	$98.77	12.688%	$111.3019	$111.30	$111.30	$111.30
7 purchase totals =	$723.14		$794.8801	$794.88	$794.80	$794.90