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	$106.39	12.495%	$119.6834	$119.68	$119.70	$119.70
Purchase #2	$208.53	11.214%	$231.9146	$231.91	$231.90	$231.90
Purchase #3	$197.70	12.171%	$221.7621	$221.76	$221.75	$221.80
Purchase #4	$59.35	3.372%	$61.3513	$61.35	$61.35	$61.40
Purchase #5	$57.38	4.128%	$59.7486	$59.75	$59.75	$59.70
Purchase #6	$41.40	9.380%	$45.2833	$45.28	$45.30	$45.30
Purchase #7	$41.45	3.570%	$42.9298	$42.93	$42.95	$42.90
7 purchase totals =	$712.20		$782.6731	$782.66	$782.70	$782.70