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	$40.45	5.290%	$42.5898	$42.59	$42.60	$42.60
Purchase #2	$198.82	12.494%	$223.6606	$223.66	$223.65	$223.70
Purchase #3	$46.27	3.166%	$47.7349	$47.73	$47.75	$47.70
Purchase #4	$99.57	10.266%	$109.7919	$109.79	$109.80	$109.80
Purchase #5	$219.65	10.326%	$242.3311	$242.33	$242.35	$242.30
Purchase #6	$87.81	10.195%	$96.7622	$96.76	$96.75	$96.80
Purchase #7	$194.34	12.732%	$219.0834	$219.08	$219.10	$219.10
7 purchase totals =	$886.91		$981.9539	$981.94	$982.00	$982.00