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	$72.47	12.822%	$81.7621	$81.76	$81.75	$81.80
Purchase #2	$92.58	4.334%	$96.5924	$96.59	$96.60	$96.60
Purchase #3	$51.27	9.733%	$56.2601	$56.26	$56.25	$56.30
Purchase #4	$139.26	9.441%	$152.4075	$152.41	$152.40	$152.40
Purchase #5	$113.33	13.170%	$128.2556	$128.26	$128.25	$128.30
Purchase #6	$139.47	9.141%	$152.219	$152.22	$152.20	$152.20
Purchase #7	$183.86	10.615%	$203.3767	$203.38	$203.40	$203.40
7 purchase totals =	$792.24		$870.8734	$870.88	$870.85	$871.00