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	$85.87	5.866%	$90.9071	$90.91	$90.90	$90.90
Purchase #2	$94.89	5.303%	$99.922	$99.92	$99.90	$99.90
Purchase #3	$84.36	6.797%	$90.0939	$90.09	$90.10	$90.10
Purchase #4	$159.67	9.293%	$174.5081	$174.51	$174.50	$174.50
Purchase #5	$183.28	4.707%	$191.907	$191.91	$191.90	$191.90
Purchase #6	$135.46	12.533%	$152.4372	$152.44	$152.45	$152.40
Purchase #7	$98.70	5.538%	$104.166	$104.17	$104.15	$104.20
7 purchase totals =	$842.23		$903.9413	$903.95	$903.90	$903.90