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	$165.70	11.328%	$184.4705	$184.47	$184.45	$184.50
Purchase #2	$233.38	12.367%	$262.2421	$262.24	$262.25	$262.20
Purchase #3	$60.76	11.700%	$67.8689	$67.87	$67.85	$67.90
Purchase #4	$22.92	12.370%	$25.7552	$25.76	$25.75	$25.80
Purchase #5	$9.73	10.791%	$10.78	$10.78	$10.80	$10.80
Purchase #6	$91.67	7.261%	$98.3262	$98.33	$98.35	$98.30
Purchase #7	$190.60	4.788%	$199.7259	$199.73	$199.75	$199.70
7 purchase totals =	$774.76		$849.1688	$849.18	$849.20	$849.20