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	$151.64	11.437%	$168.9831	$168.98	$169.00	$169.00
Purchase #2	$103.78	6.457%	$110.4811	$110.48	$110.50	$110.50
Purchase #3	$157.25	11.107%	$174.7158	$174.72	$174.70	$174.70
Purchase #4	$41.49	5.836%	$43.9114	$43.91	$43.90	$43.90
Purchase #5	$59.66	5.128%	$62.7194	$62.72	$62.70	$62.70
Purchase #6	$50.31	6.305%	$53.482	$53.48	$53.50	$53.50
Purchase #7	$111.38	7.735%	$119.9952	$120.00	$120.00	$120.00
7 purchase totals =	$675.51		$734.2880	$734.29	$734.30	$734.30