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	$103.64	6.603%	$110.4833	$110.48	$110.50	$110.50
Purchase #2	$237.57	13.435%	$269.4875	$269.49	$269.50	$269.50
Purchase #3	$206.59	8.658%	$224.4766	$224.48	$224.50	$224.50
Purchase #4	$248.82	6.566%	$265.1575	$265.16	$265.15	$265.20
Purchase #5	$247.97	3.374%	$256.3365	$256.34	$256.35	$256.30
Purchase #6	$84.82	5.381%	$89.3842	$89.38	$89.40	$89.40
Purchase #7	$142.28	5.556%	$150.1851	$150.19	$150.20	$150.20
7 purchase totals =	$1,271.69		$1,365.5107	$1,365.52	$1,365.60	$1,365.60