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	$17.88	5.450%	$18.8545	$18.85	$18.85	$18.90
Purchase #2	$147.41	13.375%	$167.1261	$167.13	$167.15	$167.10
Purchase #3	$72.66	11.270%	$80.8488	$80.85	$80.85	$80.80
Purchase #4	$111.56	7.346%	$119.7552	$119.76	$119.75	$119.80
Purchase #5	$134.91	6.200%	$143.2744	$143.27	$143.25	$143.30
Purchase #6	$90.92	4.306%	$94.835	$94.84	$94.85	$94.80
Purchase #7	$12.27	11.803%	$13.7182	$13.72	$13.70	$13.70
7 purchase totals =	$587.61		$638.4122	$638.42	$638.40	$638.40