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	$17.40	5.260%	$18.3152	$18.32	$18.30	$18.30
Purchase #2	$86.73	6.464%	$92.3362	$92.34	$92.35	$92.30
Purchase #3	$233.97	9.802%	$256.9037	$256.90	$256.90	$256.90
Purchase #4	$212.91	11.490%	$237.3734	$237.37	$237.35	$237.40
Purchase #5	$57.31	7.577%	$61.6524	$61.65	$61.65	$61.70
Purchase #6	$246.38	4.519%	$257.5139	$257.51	$257.50	$257.50
Purchase #7	$173.69	7.726%	$187.1093	$187.11	$187.10	$187.10
7 purchase totals =	$1,028.39		$1,111.2041	$1,111.20	$1,111.15	$1,111.20