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	$97.27	3.637%	$100.8077	$100.81	$100.80	$100.80
Purchase #2	$25.38	12.470%	$28.5449	$28.54	$28.55	$28.50
Purchase #3	$217.83	7.580%	$234.3415	$234.34	$234.35	$234.30
Purchase #4	$59.84	13.302%	$67.7999	$67.80	$67.80	$67.80
Purchase #5	$82.33	9.514%	$90.1629	$90.16	$90.15	$90.20
Purchase #6	$167.33	12.152%	$187.6639	$187.66	$187.65	$187.70
Purchase #7	$81.44	12.689%	$91.7739	$91.77	$91.75	$91.80
7 purchase totals =	$731.42		$801.0947	$801.08	$801.05	$801.10