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	$126.64	9.140%	$138.2149	$138.21	$138.20	$138.20
Purchase #2	$77.32	10.505%	$85.4425	$85.44	$85.45	$85.40
Purchase #3	$231.95	3.713%	$240.5623	$240.56	$240.55	$240.60
Purchase #4	$65.96	9.609%	$72.2981	$72.30	$72.30	$72.30
Purchase #5	$105.64	3.718%	$109.5677	$109.57	$109.55	$109.60
Purchase #6	$173.74	10.433%	$191.8663	$191.87	$191.85	$191.90
Purchase #7	$32.76	6.550%	$34.9058	$34.91	$34.90	$34.90
7 purchase totals =	$814.01		$872.8576	$872.86	$872.80	$872.90