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	$169.78	12.275%	$190.6205	$190.62	$190.60	$190.60
Purchase #2	$179.30	11.335%	$199.6237	$199.62	$199.60	$199.60
Purchase #3	$204.50	6.615%	$218.0277	$218.03	$218.05	$218.00
Purchase #4	$165.90	12.640%	$186.8698	$186.87	$186.85	$186.90
Purchase #5	$206.66	5.542%	$218.1131	$218.11	$218.10	$218.10
Purchase #6	$83.83	7.265%	$89.9202	$89.92	$89.90	$89.90
Purchase #7	$140.37	8.456%	$152.2397	$152.24	$152.25	$152.20
7 purchase totals =	$1,150.34		$1,255.4147	$1,255.41	$1,255.35	$1,255.30