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	$101.46	11.686%	$113.3166	$113.32	$113.30	$113.30
Purchase #2	$120.86	9.144%	$131.9114	$131.91	$131.90	$131.90
Purchase #3	$105.41	7.502%	$113.3179	$113.32	$113.30	$113.30
Purchase #4	$79.82	10.310%	$88.0494	$88.05	$88.05	$88.00
Purchase #5	$78.65	10.147%	$86.6306	$86.63	$86.65	$86.60
Purchase #6	$11.31	8.457%	$12.2665	$12.27	$12.25	$12.30
Purchase #7	$29.32	7.642%	$31.5606	$31.56	$31.55	$31.60
7 purchase totals =	$526.83		$577.0530	$577.06	$577.00	$577.00