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	$86.83	9.708%	$95.2595	$95.26	$95.25	$95.30
Purchase #2	$133.59	12.521%	$150.3168	$150.32	$150.30	$150.30
Purchase #3	$55.60	12.516%	$62.5589	$62.56	$62.55	$62.60
Purchase #4	$84.26	6.853%	$90.0343	$90.03	$90.05	$90.00
Purchase #5	$250.29	5.555%	$264.1936	$264.19	$264.20	$264.20
Purchase #6	$108.34	7.750%	$116.7364	$116.74	$116.75	$116.70
Purchase #7	$142.37	6.173%	$151.1585	$151.16	$151.15	$151.20
7 purchase totals =	$861.28		$930.2580	$930.26	$930.25	$930.30