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	$136.97	10.221%	$150.9697	$150.97	$150.95	$151.00
Purchase #2	$29.45	10.111%	$32.4277	$32.43	$32.45	$32.40
Purchase #3	$238.65	10.752%	$264.3096	$264.31	$264.30	$264.30
Purchase #4	$123.29	10.448%	$136.1713	$136.17	$136.15	$136.20
Purchase #5	$42.71	3.607%	$44.2505	$44.25	$44.25	$44.30
Purchase #6	$134.79	6.615%	$143.7064	$143.71	$143.70	$143.70
Purchase #7	$88.80	11.355%	$98.8832	$98.88	$98.90	$98.90
7 purchase totals =	$794.66		$870.7184	$870.72	$870.70	$870.80