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	$220.34	5.439%	$232.3243	$232.32	$232.30	$232.30
Purchase #2	$241.89	9.283%	$264.3446	$264.34	$264.35	$264.30
Purchase #3	$177.34	6.574%	$188.9983	$189.00	$189.00	$189.00
Purchase #4	$56.78	4.186%	$59.1568	$59.16	$59.15	$59.20
Purchase #5	$238.36	11.766%	$266.4054	$266.41	$266.40	$266.40
Purchase #6	$37.99	6.278%	$40.375	$40.38	$40.40	$40.40
Purchase #7	$199.80	7.681%	$215.1466	$215.15	$215.15	$215.10
7 purchase totals =	$1,172.50		$1,266.7510	$1,266.76	$1,266.75	$1,266.70