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	$19.67	9.669%	$21.5719	$21.57	$21.55	$21.60
Purchase #2	$199.70	11.375%	$222.4159	$222.42	$222.40	$222.40
Purchase #3	$145.67	4.119%	$151.6701	$151.67	$151.65	$151.70
Purchase #4	$197.98	12.345%	$222.4206	$222.42	$222.40	$222.40
Purchase #5	$29.34	7.130%	$31.4319	$31.43	$31.45	$31.40
Purchase #6	$210.52	4.584%	$220.1702	$220.17	$220.15	$220.20
Purchase #7	$249.49	4.155%	$259.8563	$259.86	$259.85	$259.90
7 purchase totals =	$1,052.37		$1,129.5369	$1,129.54	$1,129.45	$1,129.60