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	$238.45	4.664%	$249.5713	$249.57	$249.55	$249.60
Purchase #2	$148.69	13.312%	$168.4836	$168.48	$168.50	$168.50
Purchase #3	$89.72	13.836%	$102.1337	$102.13	$102.15	$102.10
Purchase #4	$194.95	9.111%	$212.7119	$212.71	$212.70	$212.70
Purchase #5	$153.96	13.341%	$174.4998	$174.50	$174.50	$174.50
Purchase #6	$73.88	11.556%	$82.4176	$82.42	$82.40	$82.40
Purchase #7	$68.72	11.203%	$76.4187	$76.42	$76.40	$76.40
7 purchase totals =	$968.37		$1,066.2366	$1,066.23	$1,066.20	$1,066.20