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	$17.25	6.811%	$18.4249	$18.42	$18.40	$18.40
Purchase #2	$191.59	7.612%	$206.1738	$206.17	$206.15	$206.20
Purchase #3	$206.79	8.220%	$223.7881	$223.79	$223.80	$223.80
Purchase #4	$77.89	11.570%	$86.9019	$86.90	$86.90	$86.90
Purchase #5	$115.69	11.155%	$128.5952	$128.60	$128.60	$128.60
Purchase #6	$133.43	11.116%	$148.2621	$148.26	$148.25	$148.30
Purchase #7	$42.88	12.819%	$48.3768	$48.38	$48.40	$48.40
7 purchase totals =	$785.52		$860.5228	$860.52	$860.50	$860.60