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	$25.82	9.267%	$28.2127	$28.21	$28.20	$28.20
Purchase #2	$9.89	5.406%	$10.4247	$10.42	$10.40	$10.40
Purchase #3	$112.66	13.275%	$127.6156	$127.62	$127.60	$127.60
Purchase #4	$84.97	11.191%	$94.479	$94.48	$94.50	$94.50
Purchase #5	$179.89	9.330%	$196.6737	$196.67	$196.65	$196.70
Purchase #6	$236.76	11.311%	$263.5399	$263.54	$263.55	$263.50
Purchase #7	$190.94	4.169%	$198.9003	$198.90	$198.90	$198.90
7 purchase totals =	$840.93		$919.8459	$919.84	$919.80	$919.80