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	$142.59	12.304%	$160.1343	$160.13	$160.15	$160.10
Purchase #2	$39.79	12.442%	$44.7407	$44.74	$44.75	$44.70
Purchase #3	$93.96	10.799%	$104.1067	$104.11	$104.10	$104.10
Purchase #4	$79.58	13.337%	$90.1936	$90.19	$90.20	$90.20
Purchase #5	$137.79	5.555%	$145.4442	$145.44	$145.45	$145.40
Purchase #6	$110.40	3.127%	$113.8522	$113.85	$113.85	$113.90
Purchase #7	$40.61	12.515%	$45.6923	$45.69	$45.70	$45.70
7 purchase totals =	$644.72		$704.1640	$704.15	$704.20	$704.10