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	$83.41	7.558%	$89.7141	$89.71	$89.70	$89.70
Purchase #2	$199.54	10.442%	$220.376	$220.38	$220.40	$220.40
Purchase #3	$233.47	7.749%	$251.5616	$251.56	$251.55	$251.60
Purchase #4	$96.79	13.778%	$110.1257	$110.13	$110.15	$110.10
Purchase #5	$46.71	12.738%	$52.6599	$52.66	$52.65	$52.70
Purchase #6	$215.67	10.312%	$237.9099	$237.91	$237.90	$237.90
Purchase #7	$127.81	10.721%	$141.5125	$141.51	$141.50	$141.50
7 purchase totals =	$1,003.40		$1,103.8597	$1,103.86	$1,103.85	$1,103.90