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	$31.55	4.836%	$33.0758	$33.08	$33.10	$33.10
Purchase #2	$245.26	8.813%	$266.8748	$266.87	$266.85	$266.90
Purchase #3	$32.47	10.478%	$35.8722	$35.87	$35.85	$35.90
Purchase #4	$197.75	11.378%	$220.25	$220.25	$220.25	$220.30
Purchase #5	$249.88	11.511%	$278.6437	$278.64	$278.65	$278.60
Purchase #6	$79.82	7.122%	$85.5048	$85.50	$85.50	$85.50
Purchase #7	$67.89	4.820%	$71.1623	$71.16	$71.15	$71.20
7 purchase totals =	$904.62		$991.3836	$991.37	$991.35	$991.50