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	$35.48	8.574%	$38.5221	$38.52	$38.50	$38.50
Purchase #2	$232.45	4.749%	$243.4891	$243.49	$243.50	$243.50
Purchase #3	$38.61	3.771%	$40.066	$40.07	$40.05	$40.10
Purchase #4	$171.88	8.166%	$185.9157	$185.92	$185.90	$185.90
Purchase #5	$115.83	3.536%	$119.9257	$119.93	$119.95	$119.90
Purchase #6	$98.33	13.193%	$111.3027	$111.30	$111.30	$111.30
Purchase #7	$48.47	11.616%	$54.1003	$54.10	$54.10	$54.10
7 purchase totals =	$741.05		$793.3216	$793.33	$793.30	$793.30