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	$154.82	13.746%	$176.1016	$176.10	$176.10	$176.10
Purchase #2	$107.31	6.754%	$114.5577	$114.56	$114.55	$114.60
Purchase #3	$95.97	11.403%	$106.9135	$106.91	$106.90	$106.90
Purchase #4	$217.90	12.667%	$245.5014	$245.50	$245.50	$245.50
Purchase #5	$39.97	6.612%	$42.6128	$42.61	$42.60	$42.60
Purchase #6	$67.30	3.663%	$69.7652	$69.77	$69.75	$69.80
Purchase #7	$223.29	10.538%	$246.8203	$246.82	$246.80	$246.80
7 purchase totals =	$906.56		$1,002.2725	$1,002.27	$1,002.20	$1,002.30