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	$64.97	10.704%	$71.9244	$71.92	$71.90	$71.90
Purchase #2	$249.85	3.386%	$258.3099	$258.31	$258.30	$258.30
Purchase #3	$80.77	10.439%	$89.2016	$89.20	$89.20	$89.20
Purchase #4	$78.44	10.202%	$86.4424	$86.44	$86.45	$86.40
Purchase #5	$58.34	4.809%	$61.1456	$61.15	$61.15	$61.10
Purchase #6	$81.58	10.378%	$90.0464	$90.05	$90.05	$90.00
Purchase #7	$50.53	5.328%	$53.2222	$53.22	$53.20	$53.20
7 purchase totals =	$664.48		$710.2925	$710.29	$710.25	$710.10