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	$51.67	4.589%	$54.0411	$54.04	$54.05	$54.00
Purchase #2	$147.98	4.645%	$154.8537	$154.85	$154.85	$154.90
Purchase #3	$84.75	5.789%	$89.6562	$89.66	$89.65	$89.70
Purchase #4	$124.83	5.428%	$131.6058	$131.61	$131.60	$131.60
Purchase #5	$212.59	6.811%	$227.0695	$227.07	$227.05	$227.10
Purchase #6	$15.27	5.705%	$16.1412	$16.14	$16.15	$16.10
Purchase #7	$196.76	10.116%	$216.6642	$216.66	$216.65	$216.70
7 purchase totals =	$833.85		$890.0317	$890.03	$890.00	$890.10