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	$224.92	3.780%	$233.422	$233.42	$233.40	$233.40
Purchase #2	$63.89	5.740%	$67.5573	$67.56	$67.55	$67.60
Purchase #3	$19.91	5.672%	$21.0393	$21.04	$21.05	$21.00
Purchase #4	$90.45	8.190%	$97.8579	$97.86	$97.85	$97.90
Purchase #5	$100.82	9.368%	$110.2648	$110.26	$110.25	$110.30
Purchase #6	$96.47	3.846%	$100.1802	$100.18	$100.20	$100.20
Purchase #7	$40.25	4.372%	$42.0097	$42.01	$42.00	$42.00
7 purchase totals =	$636.71		$672.3312	$672.33	$672.30	$672.40