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	$166.90	3.618%	$172.9384	$172.94	$172.95	$172.90
Purchase #2	$65.68	3.275%	$67.831	$67.83	$67.85	$67.80
Purchase #3	$50.39	5.139%	$52.9795	$52.98	$53.00	$53.00
Purchase #4	$51.65	4.476%	$53.9619	$53.96	$53.95	$54.00
Purchase #5	$73.70	7.159%	$78.9762	$78.98	$79.00	$79.00
Purchase #6	$36.81	13.104%	$41.6336	$41.63	$41.65	$41.60
Purchase #7	$233.52	4.430%	$243.8649	$243.86	$243.85	$243.90
7 purchase totals =	$678.65		$712.1855	$712.18	$712.25	$712.20