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	$10.78	5.392%	$11.3613	$11.36	$11.35	$11.40
Purchase #2	$221.69	3.288%	$228.9792	$228.98	$229.00	$229.00
Purchase #3	$159.26	7.127%	$170.6105	$170.61	$170.60	$170.60
Purchase #4	$97.91	7.267%	$105.0251	$105.03	$105.05	$105.00
Purchase #5	$187.90	4.377%	$196.1244	$196.12	$196.10	$196.10
Purchase #6	$231.94	7.254%	$248.7649	$248.76	$248.75	$248.80
Purchase #7	$128.80	8.336%	$139.5368	$139.54	$139.55	$139.50
7 purchase totals =	$1,038.28		$1,100.4022	$1,100.40	$1,100.40	$1,100.40