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	$124.53	3.465%	$128.845	$128.85	$128.85	$128.80
Purchase #2	$18.80	8.851%	$20.464	$20.46	$20.45	$20.50
Purchase #3	$19.31	8.289%	$20.9106	$20.91	$20.90	$20.90
Purchase #4	$195.91	13.617%	$222.5871	$222.59	$222.60	$222.60
Purchase #5	$18.31	7.414%	$19.6675	$19.67	$19.65	$19.70
Purchase #6	$118.63	13.574%	$134.7328	$134.73	$134.75	$134.70
Purchase #7	$108.31	3.474%	$112.0727	$112.07	$112.05	$112.10
7 purchase totals =	$603.80		$659.2797	$659.28	$659.25	$659.30