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	$78.70	6.469%	$83.7911	$83.79	$83.80	$83.80
Purchase #2	$227.31	6.236%	$241.4851	$241.49	$241.50	$241.50
Purchase #3	$91.87	9.147%	$100.2733	$100.27	$100.25	$100.30
Purchase #4	$249.34	7.545%	$268.1527	$268.15	$268.15	$268.20
Purchase #5	$227.34	6.131%	$241.2782	$241.28	$241.30	$241.30
Purchase #6	$18.70	9.843%	$20.5406	$20.54	$20.55	$20.50
Purchase #7	$216.99	5.254%	$228.3907	$228.39	$228.40	$228.40
7 purchase totals =	$1,110.25		$1,183.9117	$1,183.91	$1,183.95	$1,184.00