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	$143.83	5.347%	$151.5206	$151.52	$151.50	$151.50
Purchase #2	$156.53	7.196%	$167.7939	$167.79	$167.80	$167.80
Purchase #3	$225.65	7.270%	$242.0548	$242.05	$242.05	$242.10
Purchase #4	$14.48	4.177%	$15.0848	$15.08	$15.10	$15.10
Purchase #5	$39.77	3.280%	$41.0745	$41.07	$41.05	$41.10
Purchase #6	$62.65	7.212%	$67.1683	$67.17	$67.15	$67.20
Purchase #7	$167.51	3.342%	$173.1082	$173.11	$173.10	$173.10
7 purchase totals =	$810.42		$857.8051	$857.79	$857.75	$857.90