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	$130.87	10.236%	$144.2659	$144.27	$144.25	$144.30
Purchase #2	$33.58	10.538%	$37.1187	$37.12	$37.10	$37.10
Purchase #3	$25.91	13.755%	$29.4739	$29.47	$29.45	$29.50
Purchase #4	$145.38	10.590%	$160.7757	$160.78	$160.80	$160.80
Purchase #5	$69.73	6.366%	$74.169	$74.17	$74.15	$74.20
Purchase #6	$109.52	12.681%	$123.4082	$123.41	$123.40	$123.40
Purchase #7	$76.88	12.322%	$86.3532	$86.35	$86.35	$86.40
7 purchase totals =	$591.87		$655.5646	$655.57	$655.50	$655.70