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	$81.36	10.322%	$89.758	$89.76	$89.75	$89.80
Purchase #2	$227.59	10.405%	$251.2707	$251.27	$251.25	$251.30
Purchase #3	$185.85	12.657%	$209.373	$209.37	$209.35	$209.40
Purchase #4	$64.46	12.378%	$72.4389	$72.44	$72.45	$72.40
Purchase #5	$121.93	8.102%	$131.8088	$131.81	$131.80	$131.80
Purchase #6	$145.97	7.854%	$157.4345	$157.43	$157.45	$157.40
Purchase #7	$86.69	11.243%	$96.4366	$96.44	$96.45	$96.40
7 purchase totals =	$913.85		$1,008.5205	$1,008.52	$1,008.50	$1,008.50