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	$35.96	13.328%	$40.7527	$40.75	$40.75	$40.80
Purchase #2	$140.90	6.830%	$150.5235	$150.52	$150.50	$150.50
Purchase #3	$228.47	9.431%	$250.017	$250.02	$250.00	$250.00
Purchase #4	$49.46	10.317%	$54.5628	$54.56	$54.55	$54.60
Purchase #5	$47.63	5.771%	$50.3787	$50.38	$50.40	$50.40
Purchase #6	$246.28	8.231%	$266.5513	$266.55	$266.55	$266.60
Purchase #7	$79.50	11.538%	$88.6727	$88.67	$88.65	$88.70
7 purchase totals =	$828.20		$901.4587	$901.45	$901.40	$901.60