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	$71.83	10.589%	$79.4361	$79.44	$79.45	$79.40
Purchase #2	$151.32	12.578%	$170.353	$170.35	$170.35	$170.40
Purchase #3	$103.85	11.340%	$115.6266	$115.63	$115.65	$115.60
Purchase #4	$127.46	12.788%	$143.7596	$143.76	$143.75	$143.80
Purchase #5	$83.30	6.626%	$88.8195	$88.82	$88.80	$88.80
Purchase #6	$44.39	3.192%	$45.8069	$45.81	$45.80	$45.80
Purchase #7	$148.90	11.820%	$166.5	$166.50	$166.50	$166.50
7 purchase totals =	$731.05		$810.3017	$810.31	$810.30	$810.30