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	$156.54	6.281%	$166.3723	$166.37	$166.35	$166.40
Purchase #2	$81.96	3.797%	$85.072	$85.07	$85.05	$85.10
Purchase #3	$95.36	4.132%	$99.3003	$99.30	$99.30	$99.30
Purchase #4	$10.43	12.623%	$11.7466	$11.75	$11.75	$11.70
Purchase #5	$231.94	3.492%	$240.0393	$240.04	$240.05	$240.00
Purchase #6	$63.95	4.357%	$66.7363	$66.74	$66.75	$66.70
Purchase #7	$166.29	7.806%	$179.2706	$179.27	$179.25	$179.30
7 purchase totals =	$806.47		$848.5374	$848.54	$848.50	$848.50