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	$196.53	3.435%	$203.2808	$203.28	$203.30	$203.30
Purchase #2	$127.66	11.109%	$141.8417	$141.84	$141.85	$141.80
Purchase #3	$157.72	7.357%	$169.3235	$169.32	$169.30	$169.30
Purchase #4	$228.74	6.841%	$244.3881	$244.39	$244.40	$244.40
Purchase #5	$39.78	9.720%	$43.6466	$43.65	$43.65	$43.60
Purchase #6	$227.53	5.182%	$239.3206	$239.32	$239.30	$239.30
Purchase #7	$104.89	4.400%	$109.5052	$109.51	$109.50	$109.50
7 purchase totals =	$1,082.85		$1,151.3065	$1,151.31	$1,151.30	$1,151.20