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	$70.55	6.752%	$75.3135	$75.31	$75.30	$75.30
Purchase #2	$86.97	4.706%	$91.0628	$91.06	$91.05	$91.10
Purchase #3	$115.33	5.151%	$121.2706	$121.27	$121.25	$121.30
Purchase #4	$205.97	8.513%	$223.5042	$223.50	$223.50	$223.50
Purchase #5	$238.28	7.649%	$256.506	$256.51	$256.50	$256.50
Purchase #6	$57.72	3.801%	$59.9139	$59.91	$59.90	$59.90
Purchase #7	$26.86	7.734%	$28.9374	$28.94	$28.95	$28.90
7 purchase totals =	$801.68		$856.5084	$856.50	$856.45	$856.50