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	$230.36	8.694%	$250.3875	$250.39	$250.40	$250.40
Purchase #2	$161.46	12.614%	$181.8266	$181.83	$181.85	$181.80
Purchase #3	$140.67	9.405%	$153.9	$153.90	$153.90	$153.90
Purchase #4	$123.71	6.414%	$131.6448	$131.64	$131.65	$131.60
Purchase #5	$33.40	8.289%	$36.1685	$36.17	$36.15	$36.20
Purchase #6	$136.76	9.603%	$149.8931	$149.89	$149.90	$149.90
Purchase #7	$123.25	3.182%	$127.1718	$127.17	$127.15	$127.20
7 purchase totals =	$949.61		$1,030.9923	$1,030.99	$1,031.00	$1,031.00