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	$26.59	8.617%	$28.8813	$28.88	$28.90	$28.90
Purchase #2	$53.64	10.489%	$59.2663	$59.27	$59.25	$59.30
Purchase #3	$115.98	6.530%	$123.5535	$123.55	$123.55	$123.60
Purchase #4	$246.45	4.469%	$257.4639	$257.46	$257.45	$257.50
Purchase #5	$82.90	3.811%	$86.0593	$86.06	$86.05	$86.10
Purchase #6	$172.90	5.777%	$182.8884	$182.89	$182.90	$182.90
Purchase #7	$39.89	5.456%	$42.0664	$42.07	$42.05	$42.10
7 purchase totals =	$738.35		$780.1791	$780.18	$780.15	$780.40