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	$84.70	5.194%	$89.0993	$89.10	$89.10	$89.10
Purchase #2	$43.82	13.591%	$49.7756	$49.78	$49.80	$49.80
Purchase #3	$110.82	6.459%	$117.9779	$117.98	$118.00	$118.00
Purchase #4	$99.61	7.106%	$106.6883	$106.69	$106.70	$106.70
Purchase #5	$123.46	9.728%	$135.4702	$135.47	$135.45	$135.50
Purchase #6	$105.35	6.139%	$111.8174	$111.82	$111.80	$111.80
Purchase #7	$115.38	9.245%	$126.0469	$126.05	$126.05	$126.00
7 purchase totals =	$683.14		$736.8756	$736.89	$736.90	$736.90