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	$249.92	10.658%	$276.5565	$276.56	$276.55	$276.60
Purchase #2	$179.96	11.764%	$201.1305	$201.13	$201.15	$201.10
Purchase #3	$35.94	13.221%	$40.6916	$40.69	$40.70	$40.70
Purchase #4	$222.78	8.304%	$241.2797	$241.28	$241.30	$241.30
Purchase #5	$196.85	5.830%	$208.3264	$208.33	$208.35	$208.30
Purchase #6	$101.52	9.818%	$111.4872	$111.49	$111.50	$111.50
Purchase #7	$106.35	5.481%	$112.179	$112.18	$112.20	$112.20
7 purchase totals =	$1,093.32		$1,191.6509	$1,191.66	$1,191.75	$1,191.70