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	$50.46	10.418%	$55.7169	$55.72	$55.70	$55.70
Purchase #2	$158.73	7.771%	$171.0649	$171.06	$171.05	$171.10
Purchase #3	$117.92	6.315%	$125.3666	$125.37	$125.35	$125.40
Purchase #4	$190.67	13.651%	$216.6984	$216.70	$216.70	$216.70
Purchase #5	$206.86	4.114%	$215.3702	$215.37	$215.35	$215.40
Purchase #6	$98.84	12.871%	$111.5617	$111.56	$111.55	$111.60
Purchase #7	$64.32	13.302%	$72.8758	$72.88	$72.90	$72.90
7 purchase totals =	$887.80		$968.6545	$968.66	$968.60	$968.80