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	$232.80	13.472%	$264.1628	$264.16	$264.15	$264.20
Purchase #2	$189.83	4.765%	$198.8754	$198.88	$198.90	$198.90
Purchase #3	$97.32	12.773%	$109.7507	$109.75	$109.75	$109.80
Purchase #4	$96.30	3.585%	$99.7524	$99.75	$99.75	$99.80
Purchase #5	$77.75	10.187%	$85.6704	$85.67	$85.65	$85.70
Purchase #6	$17.81	5.687%	$18.8229	$18.82	$18.80	$18.80
Purchase #7	$55.52	11.773%	$62.0564	$62.06	$62.05	$62.10
7 purchase totals =	$767.33		$839.0910	$839.09	$839.05	$839.30