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	$120.95	13.180%	$136.8912	$136.89	$136.90	$136.90
Purchase #2	$122.56	12.120%	$137.4143	$137.41	$137.40	$137.40
Purchase #3	$89.67	8.195%	$97.0185	$97.02	$97.00	$97.00
Purchase #4	$86.50	5.727%	$91.4539	$91.45	$91.45	$91.50
Purchase #5	$61.51	9.520%	$67.3658	$67.37	$67.35	$67.40
Purchase #6	$132.49	6.275%	$140.8037	$140.80	$140.80	$140.80
Purchase #7	$31.85	4.770%	$33.3692	$33.37	$33.35	$33.40
7 purchase totals =	$645.53		$704.3166	$704.31	$704.25	$704.40