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	$88.62	4.577%	$92.6761	$92.68	$92.70	$92.70
Purchase #2	$202.34	11.272%	$225.1478	$225.15	$225.15	$225.10
Purchase #3	$105.45	8.516%	$114.4301	$114.43	$114.45	$114.40
Purchase #4	$247.75	10.650%	$274.1354	$274.14	$274.15	$274.10
Purchase #5	$166.55	11.570%	$185.8198	$185.82	$185.80	$185.80
Purchase #6	$11.40	9.113%	$12.4389	$12.44	$12.45	$12.40
Purchase #7	$87.25	12.398%	$98.0673	$98.07	$98.05	$98.10
7 purchase totals =	$909.36		$1,002.7154	$1,002.73	$1,002.75	$1,002.60