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	$121.78	8.319%	$131.9109	$131.91	$131.90	$131.90
Purchase #2	$216.82	5.666%	$229.105	$229.11	$229.10	$229.10
Purchase #3	$128.29	12.736%	$144.629	$144.63	$144.65	$144.60
Purchase #4	$243.92	3.474%	$252.3938	$252.39	$252.40	$252.40
Purchase #5	$109.94	4.294%	$114.6608	$114.66	$114.65	$114.70
Purchase #6	$34.32	3.333%	$35.4639	$35.46	$35.45	$35.50
Purchase #7	$217.64	11.175%	$241.9613	$241.96	$241.95	$242.00
7 purchase totals =	$1,072.71		$1,150.1247	$1,150.12	$1,150.10	$1,150.20