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	$210.43	4.783%	$220.4949	$220.49	$220.50	$220.50
Purchase #2	$134.90	5.524%	$142.3519	$142.35	$142.35	$142.40
Purchase #3	$139.32	4.166%	$145.1241	$145.12	$145.10	$145.10
Purchase #4	$85.38	7.281%	$91.5965	$91.60	$91.60	$91.60
Purchase #5	$116.32	12.561%	$130.931	$130.93	$130.95	$130.90
Purchase #6	$242.72	9.865%	$266.6643	$266.66	$266.65	$266.70
Purchase #7	$41.65	4.512%	$43.5292	$43.53	$43.55	$43.50
7 purchase totals =	$970.72		$1,040.6919	$1,040.68	$1,040.70	$1,040.70