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	$227.72	6.226%	$241.8978	$241.90	$241.90	$241.90
Purchase #2	$108.45	6.525%	$115.5264	$115.53	$115.55	$115.50
Purchase #3	$89.76	6.745%	$95.8143	$95.81	$95.80	$95.80
Purchase #4	$168.35	10.419%	$185.8904	$185.89	$185.90	$185.90
Purchase #5	$41.33	4.780%	$43.3056	$43.31	$43.30	$43.30
Purchase #6	$53.90	13.140%	$60.9825	$60.98	$61.00	$61.00
Purchase #7	$106.93	8.687%	$116.219	$116.22	$116.20	$116.20
7 purchase totals =	$796.44		$859.6360	$859.64	$859.65	$859.60