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	$18.50	10.139%	$20.3757	$20.38	$20.40	$20.40
Purchase #2	$246.44	11.132%	$273.8737	$273.87	$273.85	$273.90
Purchase #3	$28.97	9.608%	$31.7534	$31.75	$31.75	$31.80
Purchase #4	$152.60	3.503%	$157.9456	$157.95	$157.95	$157.90
Purchase #5	$176.79	7.555%	$190.1465	$190.15	$190.15	$190.10
Purchase #6	$223.42	13.640%	$253.8945	$253.89	$253.90	$253.90
Purchase #7	$127.32	5.334%	$134.1112	$134.11	$134.10	$134.10
7 purchase totals =	$974.04		$1,062.1006	$1,062.10	$1,062.10	$1,062.10