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	$173.79	4.131%	$180.9693	$180.97	$180.95	$181.00
Purchase #2	$99.90	3.329%	$103.2257	$103.23	$103.25	$103.20
Purchase #3	$33.76	7.793%	$36.3909	$36.39	$36.40	$36.40
Purchase #4	$66.57	9.484%	$72.8835	$72.88	$72.90	$72.90
Purchase #5	$90.59	4.505%	$94.6711	$94.67	$94.65	$94.70
Purchase #6	$10.55	12.422%	$11.8605	$11.86	$11.85	$11.90
Purchase #7	$123.96	6.346%	$131.8265	$131.83	$131.85	$131.80
7 purchase totals =	$599.12		$631.8275	$631.83	$631.85	$631.90