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	$233.49	13.432%	$264.8524	$264.85	$264.85	$264.90
Purchase #2	$191.44	4.636%	$200.3152	$200.32	$200.30	$200.30
Purchase #3	$146.77	8.823%	$159.7195	$159.72	$159.70	$159.70
Purchase #4	$115.69	11.179%	$128.623	$128.62	$128.60	$128.60
Purchase #5	$245.72	8.424%	$266.4195	$266.42	$266.40	$266.40
Purchase #6	$168.84	10.528%	$186.6155	$186.62	$186.60	$186.60
Purchase #7	$133.51	12.658%	$150.4097	$150.41	$150.40	$150.40
7 purchase totals =	$1,235.46		$1,356.9548	$1,356.96	$1,356.85	$1,356.90