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	$107.76	3.279%	$111.2935	$111.29	$111.30	$111.30
Purchase #2	$188.33	5.347%	$198.4	$198.40	$198.40	$198.40
Purchase #3	$16.89	10.483%	$18.6606	$18.66	$18.65	$18.70
Purchase #4	$209.29	13.232%	$236.9833	$236.98	$237.00	$237.00
Purchase #5	$182.62	11.772%	$204.118	$204.12	$204.10	$204.10
Purchase #6	$39.61	6.590%	$42.2203	$42.22	$42.20	$42.20
Purchase #7	$75.82	9.196%	$82.7924	$82.79	$82.80	$82.80
7 purchase totals =	$820.32		$894.4681	$894.46	$894.45	$894.50