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	$139.75	5.838%	$147.9086	$147.91	$147.90	$147.90
Purchase #2	$227.40	7.224%	$243.8274	$243.83	$243.85	$243.80
Purchase #3	$118.39	7.621%	$127.4125	$127.41	$127.40	$127.40
Purchase #4	$185.40	7.811%	$199.8816	$199.88	$199.90	$199.90
Purchase #5	$92.82	10.714%	$102.7647	$102.76	$102.75	$102.80
Purchase #6	$48.76	3.365%	$50.4008	$50.40	$50.40	$50.40
Purchase #7	$122.73	3.712%	$127.2857	$127.29	$127.30	$127.30
7 purchase totals =	$935.25		$999.4813	$999.48	$999.50	$999.50