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	$187.69	6.720%	$200.3028	$200.30	$200.30	$200.30
Purchase #2	$231.63	9.573%	$253.8039	$253.80	$253.80	$253.80
Purchase #3	$182.66	4.693%	$191.2322	$191.23	$191.25	$191.20
Purchase #4	$116.36	13.719%	$132.3234	$132.32	$132.30	$132.30
Purchase #5	$64.55	9.278%	$70.5389	$70.54	$70.55	$70.50
Purchase #6	$54.40	13.767%	$61.8892	$61.89	$61.90	$61.90
Purchase #7	$201.53	13.233%	$228.1985	$228.20	$228.20	$228.20
7 purchase totals =	$1,038.82		$1,138.2889	$1,138.28	$1,138.30	$1,138.20