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	$74.81	5.316%	$78.7869	$78.79	$78.80	$78.80
Purchase #2	$244.83	10.405%	$270.3046	$270.30	$270.30	$270.30
Purchase #3	$195.57	12.424%	$219.8676	$219.87	$219.85	$219.90
Purchase #4	$132.75	3.863%	$137.8781	$137.88	$137.90	$137.90
Purchase #5	$222.56	4.572%	$232.7354	$232.74	$232.75	$232.70
Purchase #6	$33.86	10.763%	$37.5044	$37.50	$37.50	$37.50
Purchase #7	$159.49	4.410%	$166.5235	$166.52	$166.50	$166.50
7 purchase totals =	$1,063.87		$1,143.6005	$1,143.60	$1,143.60	$1,143.60