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	$204.67	8.868%	$222.8201	$222.82	$222.80	$222.80
Purchase #2	$124.89	10.107%	$137.5126	$137.51	$137.50	$137.50
Purchase #3	$77.82	13.490%	$88.3179	$88.32	$88.30	$88.30
Purchase #4	$166.65	6.494%	$177.4723	$177.47	$177.45	$177.50
Purchase #5	$116.46	9.799%	$127.8719	$127.87	$127.85	$127.90
Purchase #6	$76.54	10.160%	$84.3165	$84.32	$84.30	$84.30
Purchase #7	$83.41	3.383%	$86.2318	$86.23	$86.25	$86.20
7 purchase totals =	$850.44		$924.5431	$924.54	$924.45	$924.50