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	$33.92	10.237%	$37.3924	$37.39	$37.40	$37.40
Purchase #2	$42.81	9.219%	$46.7567	$46.76	$46.75	$46.80
Purchase #3	$132.84	6.268%	$141.1664	$141.17	$141.15	$141.20
Purchase #4	$127.73	11.332%	$142.2044	$142.20	$142.20	$142.20
Purchase #5	$177.56	7.276%	$190.4793	$190.48	$190.50	$190.50
Purchase #6	$200.84	9.249%	$219.4157	$219.42	$219.40	$219.40
Purchase #7	$71.82	3.528%	$74.3538	$74.35	$74.35	$74.40
7 purchase totals =	$787.52		$851.7687	$851.77	$851.75	$851.90