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	$100.35	11.489%	$111.8792	$111.88	$111.90	$111.90
Purchase #2	$14.45	10.246%	$15.9305	$15.93	$15.95	$15.90
Purchase #3	$82.64	10.647%	$91.4387	$91.44	$91.45	$91.40
Purchase #4	$150.50	10.140%	$165.7607	$165.76	$165.75	$165.80
Purchase #5	$17.47	4.135%	$18.1924	$18.19	$18.20	$18.20
Purchase #6	$123.53	3.840%	$128.2736	$128.27	$128.25	$128.30
Purchase #7	$152.71	3.313%	$157.7693	$157.77	$157.75	$157.80
7 purchase totals =	$641.65		$689.2444	$689.24	$689.25	$689.30