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	$62.49	3.673%	$64.7853	$64.79	$64.80	$64.80
Purchase #2	$61.99	8.283%	$67.1246	$67.12	$67.10	$67.10
Purchase #3	$211.32	7.381%	$226.9175	$226.92	$226.90	$226.90
Purchase #4	$93.99	12.620%	$105.8515	$105.85	$105.85	$105.90
Purchase #5	$47.77	6.331%	$50.7943	$50.79	$50.80	$50.80
Purchase #6	$75.88	3.824%	$78.7817	$78.78	$78.80	$78.80
Purchase #7	$32.46	10.544%	$35.8826	$35.88	$35.90	$35.90
7 purchase totals =	$585.90		$630.1375	$630.13	$630.15	$630.20