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	$116.81	3.538%	$120.9427	$120.94	$120.95	$120.90
Purchase #2	$89.75	10.781%	$99.4259	$99.43	$99.45	$99.40
Purchase #3	$230.87	10.117%	$254.2271	$254.23	$254.25	$254.20
Purchase #4	$145.25	3.197%	$149.8936	$149.89	$149.90	$149.90
Purchase #5	$77.29	8.521%	$83.8759	$83.88	$83.90	$83.90
Purchase #6	$39.35	3.285%	$40.6426	$40.64	$40.65	$40.60
Purchase #7	$31.70	12.377%	$35.6235	$35.62	$35.60	$35.60
7 purchase totals =	$731.02		$784.6313	$784.63	$784.70	$784.50