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	$25.72	5.658%	$27.1752	$27.18	$27.20	$27.20
Purchase #2	$61.50	4.440%	$64.2306	$64.23	$64.25	$64.20
Purchase #3	$117.58	4.702%	$123.1086	$123.11	$123.10	$123.10
Purchase #4	$50.86	6.749%	$54.2925	$54.29	$54.30	$54.30
Purchase #5	$41.50	7.492%	$44.6092	$44.61	$44.60	$44.60
Purchase #6	$58.86	13.815%	$66.9915	$66.99	$67.00	$67.00
Purchase #7	$6.32	11.759%	$7.0632	$7.06	$7.05	$7.10
7 purchase totals =	$362.34		$387.4708	$387.47	$387.50	$387.50