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	$165.42	3.655%	$171.4661	$171.47	$171.45	$171.50
Purchase #2	$131.87	7.560%	$141.8394	$141.84	$141.85	$141.80
Purchase #3	$60.26	3.164%	$62.1666	$62.17	$62.15	$62.20
Purchase #4	$106.26	12.704%	$119.7593	$119.76	$119.75	$119.80
Purchase #5	$170.47	6.327%	$181.2556	$181.26	$181.25	$181.30
Purchase #6	$164.45	13.395%	$186.4781	$186.48	$186.50	$186.50
Purchase #7	$56.78	10.571%	$62.7822	$62.78	$62.80	$62.80
7 purchase totals =	$855.51		$925.7473	$925.76	$925.75	$925.90