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	$34.57	9.107%	$37.7183	$37.72	$37.70	$37.70
Purchase #2	$8.66	11.436%	$9.6504	$9.65	$9.65	$9.70
Purchase #3	$145.53	7.760%	$156.8231	$156.82	$156.80	$156.80
Purchase #4	$44.69	12.834%	$50.4255	$50.43	$50.45	$50.40
Purchase #5	$131.91	13.786%	$150.0951	$150.10	$150.10	$150.10
Purchase #6	$116.65	9.334%	$127.5381	$127.54	$127.55	$127.50
Purchase #7	$246.90	6.590%	$263.1707	$263.17	$263.15	$263.20
7 purchase totals =	$728.91		$795.4212	$795.43	$795.40	$795.40