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	$123.67	8.253%	$133.8765	$133.88	$133.90	$133.90
Purchase #2	$194.79	4.618%	$203.7854	$203.79	$203.80	$203.80
Purchase #3	$26.34	9.118%	$28.7417	$28.74	$28.75	$28.70
Purchase #4	$82.73	9.254%	$90.3858	$90.39	$90.40	$90.40
Purchase #5	$37.57	5.517%	$39.6427	$39.64	$39.65	$39.60
Purchase #6	$77.71	5.838%	$82.2467	$82.25	$82.25	$82.20
Purchase #7	$65.71	8.484%	$71.2848	$71.28	$71.30	$71.30
7 purchase totals =	$608.52		$649.9636	$649.97	$650.05	$649.90