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	$199.70	5.566%	$210.8153	$210.82	$210.80	$210.80
Purchase #2	$170.91	11.641%	$190.8056	$190.81	$190.80	$190.80
Purchase #3	$102.77	6.502%	$109.4521	$109.45	$109.45	$109.50
Purchase #4	$249.79	5.784%	$264.2379	$264.24	$264.25	$264.20
Purchase #5	$38.59	4.581%	$40.3578	$40.36	$40.35	$40.40
Purchase #6	$10.39	12.853%	$11.7254	$11.73	$11.75	$11.70
Purchase #7	$174.30	5.130%	$183.2416	$183.24	$183.25	$183.20
7 purchase totals =	$946.45		$1,010.6357	$1,010.65	$1,010.65	$1,010.60