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	$109.82	3.387%	$113.5396	$113.54	$113.55	$113.50
Purchase #2	$118.76	3.679%	$123.1292	$123.13	$123.15	$123.10
Purchase #3	$78.81	4.129%	$82.0641	$82.06	$82.05	$82.10
Purchase #4	$213.49	6.173%	$226.6687	$226.67	$226.65	$226.70
Purchase #5	$112.48	9.728%	$123.4221	$123.42	$123.40	$123.40
Purchase #6	$155.25	5.822%	$164.2887	$164.29	$164.30	$164.30
Purchase #7	$131.49	11.628%	$146.7797	$146.78	$146.80	$146.80
7 purchase totals =	$920.10		$979.8921	$979.89	$979.90	$979.90