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	$205.78	5.607%	$217.3181	$217.32	$217.30	$217.30
Purchase #2	$220.76	12.143%	$247.5669	$247.57	$247.55	$247.60
Purchase #3	$123.88	4.223%	$129.1115	$129.11	$129.10	$129.10
Purchase #4	$65.93	9.558%	$72.2316	$72.23	$72.25	$72.20
Purchase #5	$119.43	6.765%	$127.5094	$127.51	$127.50	$127.50
Purchase #6	$77.71	12.653%	$87.5426	$87.54	$87.55	$87.50
Purchase #7	$82.87	10.751%	$91.7794	$91.78	$91.80	$91.80
7 purchase totals =	$896.36		$973.0595	$973.06	$973.05	$973.00