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	$124.92	11.794%	$139.6531	$139.65	$139.65	$139.70
Purchase #2	$219.82	3.636%	$227.8127	$227.81	$227.80	$227.80
Purchase #3	$80.46	10.594%	$88.9839	$88.98	$89.00	$89.00
Purchase #4	$88.98	11.616%	$99.3159	$99.32	$99.30	$99.30
Purchase #5	$208.36	10.494%	$230.2253	$230.23	$230.25	$230.20
Purchase #6	$127.37	12.174%	$142.876	$142.88	$142.90	$142.90
Purchase #7	$182.53	7.186%	$195.6466	$195.65	$195.65	$195.60
7 purchase totals =	$1,032.44		$1,124.5135	$1,124.52	$1,124.55	$1,124.50