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	$86.52	4.810%	$90.6816	$90.68	$90.70	$90.70
Purchase #2	$156.34	6.806%	$166.9805	$166.98	$167.00	$167.00
Purchase #3	$82.53	3.862%	$85.7173	$85.72	$85.70	$85.70
Purchase #4	$198.34	5.620%	$209.4867	$209.49	$209.50	$209.50
Purchase #5	$74.90	10.329%	$82.6364	$82.64	$82.65	$82.60
Purchase #6	$176.54	7.457%	$189.7046	$189.70	$189.70	$189.70
Purchase #7	$14.76	9.586%	$16.1749	$16.17	$16.15	$16.20
7 purchase totals =	$789.93		$841.3820	$841.38	$841.40	$841.40