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	$37.31	13.200%	$42.2349	$42.23	$42.25	$42.20
Purchase #2	$77.42	12.760%	$87.2988	$87.30	$87.30	$87.30
Purchase #3	$198.69	12.207%	$222.9441	$222.94	$222.95	$222.90
Purchase #4	$36.85	6.296%	$39.1701	$39.17	$39.15	$39.20
Purchase #5	$181.65	10.267%	$200.3	$200.30	$200.30	$200.30
Purchase #6	$62.78	7.244%	$67.3278	$67.33	$67.35	$67.30
Purchase #7	$112.84	4.621%	$118.0543	$118.05	$118.05	$118.10
7 purchase totals =	$707.54		$777.3300	$777.32	$777.35	$777.30