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	$130.32	5.766%	$137.8343	$137.83	$137.85	$137.80
Purchase #2	$243.80	5.648%	$257.5698	$257.57	$257.55	$257.60
Purchase #3	$44.91	10.148%	$49.4675	$49.47	$49.45	$49.50
Purchase #4	$216.55	9.407%	$236.9209	$236.92	$236.90	$236.90
Purchase #5	$41.36	11.766%	$46.2264	$46.23	$46.25	$46.20
Purchase #6	$65.33	9.605%	$71.6049	$71.60	$71.60	$71.60
Purchase #7	$188.27	6.690%	$200.8653	$200.87	$200.85	$200.90
7 purchase totals =	$930.54		$1,000.4891	$1,000.49	$1,000.45	$1,000.50