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	$26.61	8.362%	$28.8351	$28.84	$28.85	$28.80
Purchase #2	$174.88	11.567%	$195.1084	$195.11	$195.10	$195.10
Purchase #3	$54.33	9.162%	$59.3077	$59.31	$59.30	$59.30
Purchase #4	$70.38	9.305%	$76.9289	$76.93	$76.95	$76.90
Purchase #5	$242.71	8.580%	$263.5345	$263.53	$263.55	$263.50
Purchase #6	$30.45	3.800%	$31.6071	$31.61	$31.60	$31.60
Purchase #7	$10.57	11.406%	$11.7756	$11.78	$11.80	$11.80
7 purchase totals =	$609.93		$667.0973	$667.11	$667.15	$667.00