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	$37.93	4.187%	$39.5181	$39.52	$39.50	$39.50
Purchase #2	$79.97	3.132%	$82.4747	$82.47	$82.45	$82.50
Purchase #3	$29.56	13.300%	$33.4915	$33.49	$33.50	$33.50
Purchase #4	$191.54	4.555%	$200.2646	$200.26	$200.25	$200.30
Purchase #5	$187.93	3.279%	$194.0922	$194.09	$194.10	$194.10
Purchase #6	$89.26	7.411%	$95.8751	$95.88	$95.90	$95.90
Purchase #7	$133.69	4.251%	$139.3732	$139.37	$139.35	$139.40
7 purchase totals =	$749.88		$785.0894	$785.08	$785.05	$785.20