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	$26.45	5.450%	$27.8915	$27.89	$27.90	$27.90
Purchase #2	$167.73	9.374%	$183.453	$183.45	$183.45	$183.50
Purchase #3	$184.47	5.375%	$194.3853	$194.39	$194.40	$194.40
Purchase #4	$160.52	8.753%	$174.5703	$174.57	$174.55	$174.60
Purchase #5	$81.76	5.785%	$86.4898	$86.49	$86.50	$86.50
Purchase #6	$95.90	3.688%	$99.4368	$99.44	$99.45	$99.40
Purchase #7	$63.83	3.453%	$66.034	$66.03	$66.05	$66.00
7 purchase totals =	$780.66		$832.2607	$832.26	$832.30	$832.30