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	$127.44	3.358%	$131.7194	$131.72	$131.70	$131.70
Purchase #2	$215.46	11.752%	$240.7809	$240.78	$240.80	$240.80
Purchase #3	$109.98	4.479%	$114.906	$114.91	$114.90	$114.90
Purchase #4	$132.85	12.285%	$149.1706	$149.17	$149.15	$149.20
Purchase #5	$13.54	6.749%	$14.4538	$14.45	$14.45	$14.50
Purchase #6	$208.91	12.837%	$235.7278	$235.73	$235.75	$235.70
Purchase #7	$86.41	6.593%	$92.107	$92.11	$92.10	$92.10
7 purchase totals =	$894.59		$978.8655	$978.87	$978.85	$978.90