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	$209.53	3.320%	$216.4864	$216.49	$216.50	$216.50
Purchase #2	$118.62	8.263%	$128.4216	$128.42	$128.40	$128.40
Purchase #3	$181.51	9.428%	$198.6228	$198.62	$198.60	$198.60
Purchase #4	$174.37	9.241%	$190.4835	$190.48	$190.50	$190.50
Purchase #5	$231.86	9.552%	$254.0073	$254.01	$254.00	$254.00
Purchase #6	$106.80	11.297%	$118.8652	$118.87	$118.85	$118.90
Purchase #7	$63.59	6.658%	$67.8238	$67.82	$67.80	$67.80
7 purchase totals =	$1,086.28		$1,174.7106	$1,174.71	$1,174.65	$1,174.70