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	$54.71	11.152%	$60.8113	$60.81	$60.80	$60.80
Purchase #2	$209.66	6.275%	$222.8162	$222.82	$222.80	$222.80
Purchase #3	$110.72	5.560%	$116.876	$116.88	$116.90	$116.90
Purchase #4	$134.95	11.556%	$150.5448	$150.54	$150.55	$150.50
Purchase #5	$65.35	9.174%	$71.3452	$71.35	$71.35	$71.30
Purchase #6	$104.67	8.444%	$113.5083	$113.51	$113.50	$113.50
Purchase #7	$171.68	12.262%	$192.7314	$192.73	$192.75	$192.70
7 purchase totals =	$851.74		$928.6332	$928.64	$928.65	$928.50