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	$232.65	9.599%	$254.9821	$254.98	$255.00	$255.00
Purchase #2	$246.76	6.303%	$262.3133	$262.31	$262.30	$262.30
Purchase #3	$180.91	3.307%	$186.8927	$186.89	$186.90	$186.90
Purchase #4	$144.49	6.279%	$153.5625	$153.56	$153.55	$153.60
Purchase #5	$191.69	13.614%	$217.7867	$217.79	$217.80	$217.80
Purchase #6	$46.36	12.528%	$52.168	$52.17	$52.15	$52.20
Purchase #7	$144.46	5.301%	$152.1178	$152.12	$152.10	$152.10
7 purchase totals =	$1,187.32		$1,279.8231	$1,279.82	$1,279.80	$1,279.90