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	$36.56	12.484%	$41.1242	$41.12	$41.10	$41.10
Purchase #2	$135.87	11.834%	$151.9489	$151.95	$151.95	$151.90
Purchase #3	$184.99	8.280%	$200.3072	$200.31	$200.30	$200.30
Purchase #4	$76.49	4.263%	$79.7508	$79.75	$79.75	$79.80
Purchase #5	$97.48	3.763%	$101.1482	$101.15	$101.15	$101.10
Purchase #6	$78.83	8.722%	$85.7056	$85.71	$85.70	$85.70
Purchase #7	$69.56	3.422%	$71.9403	$71.94	$71.95	$71.90
7 purchase totals =	$679.78		$731.9252	$731.93	$731.90	$731.80