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	$37.91	11.658%	$42.3295	$42.33	$42.35	$42.30
Purchase #2	$168.40	4.480%	$175.9443	$175.94	$175.95	$175.90
Purchase #3	$226.37	6.193%	$240.3891	$240.39	$240.40	$240.40
Purchase #4	$114.31	11.170%	$127.0784	$127.08	$127.10	$127.10
Purchase #5	$228.66	11.260%	$254.4071	$254.41	$254.40	$254.40
Purchase #6	$81.43	11.591%	$90.8686	$90.87	$90.85	$90.90
Purchase #7	$52.87	8.187%	$57.1985	$57.20	$57.20	$57.20
7 purchase totals =	$909.95		$988.2155	$988.22	$988.25	$988.20