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	$203.27	3.343%	$210.0653	$210.07	$210.05	$210.10
Purchase #2	$238.92	7.550%	$256.9585	$256.96	$256.95	$257.00
Purchase #3	$194.68	12.214%	$218.4582	$218.46	$218.45	$218.50
Purchase #4	$160.40	4.666%	$167.8843	$167.88	$167.90	$167.90
Purchase #5	$92.75	7.217%	$99.4438	$99.44	$99.45	$99.40
Purchase #6	$142.72	12.694%	$160.8369	$160.84	$160.85	$160.80
Purchase #7	$196.42	12.582%	$221.1336	$221.13	$221.15	$221.10
7 purchase totals =	$1,229.16		$1,334.7806	$1,334.78	$1,334.80	$1,334.80