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	$168.73	11.590%	$188.2858	$188.29	$188.30	$188.30
Purchase #2	$52.25	13.454%	$59.2797	$59.28	$59.30	$59.30
Purchase #3	$239.53	10.368%	$264.3645	$264.36	$264.35	$264.40
Purchase #4	$236.64	12.472%	$266.1537	$266.15	$266.15	$266.20
Purchase #5	$157.66	6.172%	$167.3908	$167.39	$167.40	$167.40
Purchase #6	$85.66	7.820%	$92.3586	$92.36	$92.35	$92.40
Purchase #7	$205.48	6.832%	$219.5184	$219.52	$219.50	$219.50
7 purchase totals =	$1,145.95		$1,257.3515	$1,257.35	$1,257.35	$1,257.50