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	$139.62	7.732%	$150.4154	$150.42	$150.40	$150.40
Purchase #2	$97.30	5.628%	$102.776	$102.78	$102.80	$102.80
Purchase #3	$10.38	10.588%	$11.479	$11.48	$11.50	$11.50
Purchase #4	$15.77	3.481%	$16.319	$16.32	$16.30	$16.30
Purchase #5	$195.80	13.642%	$222.511	$222.51	$222.50	$222.50
Purchase #6	$209.91	12.767%	$236.7092	$236.71	$236.70	$236.70
Purchase #7	$120.32	6.322%	$127.9266	$127.93	$127.95	$127.90
7 purchase totals =	$789.10		$868.1362	$868.15	$868.15	$868.10