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	$70.33	11.363%	$78.3216	$78.32	$78.30	$78.30
Purchase #2	$153.62	12.279%	$172.483	$172.48	$172.50	$172.50
Purchase #3	$48.40	6.600%	$51.5944	$51.59	$51.60	$51.60
Purchase #4	$211.58	3.728%	$219.4677	$219.47	$219.45	$219.50
Purchase #5	$209.62	8.669%	$227.792	$227.79	$227.80	$227.80
Purchase #6	$138.37	7.764%	$149.113	$149.11	$149.10	$149.10
Purchase #7	$246.39	3.288%	$254.4913	$254.49	$254.50	$254.50
7 purchase totals =	$1,078.31		$1,153.2630	$1,153.25	$1,153.25	$1,153.30