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	$34.40	9.599%	$37.7021	$37.70	$37.70	$37.70
Purchase #2	$82.55	7.701%	$88.9072	$88.91	$88.90	$88.90
Purchase #3	$148.87	3.132%	$153.5326	$153.53	$153.55	$153.50
Purchase #4	$171.55	6.257%	$182.2839	$182.28	$182.30	$182.30
Purchase #5	$157.53	6.771%	$168.1964	$168.20	$168.20	$168.20
Purchase #6	$137.35	4.436%	$143.4428	$143.44	$143.45	$143.40
Purchase #7	$98.38	7.222%	$105.485	$105.49	$105.50	$105.50
7 purchase totals =	$830.63		$879.5500	$879.55	$879.60	$879.50