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	$96.51	13.846%	$109.8728	$109.87	$109.85	$109.90
Purchase #2	$125.89	9.440%	$137.774	$137.77	$137.75	$137.80
Purchase #3	$67.94	12.727%	$76.5867	$76.59	$76.60	$76.60
Purchase #4	$245.51	9.469%	$268.7573	$268.76	$268.75	$268.80
Purchase #5	$114.54	6.435%	$121.9106	$121.91	$121.90	$121.90
Purchase #6	$54.99	11.617%	$61.3782	$61.38	$61.40	$61.40
Purchase #7	$90.83	3.346%	$93.8692	$93.87	$93.85	$93.90
7 purchase totals =	$796.21		$870.1488	$870.15	$870.10	$870.30