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	$69.36	13.125%	$78.4635	$78.46	$78.45	$78.50
Purchase #2	$95.76	4.276%	$99.8547	$99.85	$99.85	$99.90
Purchase #3	$231.92	5.673%	$245.0768	$245.08	$245.10	$245.10
Purchase #4	$59.26	13.279%	$67.1291	$67.13	$67.15	$67.10
Purchase #5	$38.52	8.167%	$41.6659	$41.67	$41.65	$41.70
Purchase #6	$23.36	9.512%	$25.582	$25.58	$25.60	$25.60
Purchase #7	$62.91	10.335%	$69.4117	$69.41	$69.40	$69.40
7 purchase totals =	$581.09		$627.1837	$627.18	$627.20	$627.30