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	$163.46	13.712%	$185.8736	$185.87	$185.85	$185.90
Purchase #2	$39.85	12.120%	$44.6798	$44.68	$44.70	$44.70
Purchase #3	$232.26	13.365%	$263.3015	$263.30	$263.30	$263.30
Purchase #4	$234.97	6.428%	$250.0739	$250.07	$250.05	$250.10
Purchase #5	$141.96	4.350%	$148.1353	$148.14	$148.15	$148.10
Purchase #6	$80.84	10.579%	$89.3921	$89.39	$89.40	$89.40
Purchase #7	$97.56	7.602%	$104.9765	$104.98	$105.00	$105.00
7 purchase totals =	$990.90		$1,086.4327	$1,086.43	$1,086.45	$1,086.50