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	$228.66	12.570%	$257.4026	$257.40	$257.40	$257.40
Purchase #2	$120.39	13.246%	$136.3369	$136.34	$136.35	$136.30
Purchase #3	$27.35	4.435%	$28.563	$28.56	$28.55	$28.60
Purchase #4	$164.98	12.225%	$185.1488	$185.15	$185.15	$185.10
Purchase #5	$50.40	3.518%	$52.1731	$52.17	$52.15	$52.20
Purchase #6	$50.34	7.264%	$53.9967	$54.00	$54.00	$54.00
Purchase #7	$104.49	13.310%	$118.3976	$118.40	$118.40	$118.40
7 purchase totals =	$746.61		$832.0187	$832.02	$832.00	$832.00