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	$36.98	13.824%	$42.0921	$42.09	$42.10	$42.10
Purchase #2	$33.27	9.751%	$36.5142	$36.51	$36.50	$36.50
Purchase #3	$66.75	7.249%	$71.5887	$71.59	$71.60	$71.60
Purchase #4	$91.63	7.195%	$98.2228	$98.22	$98.20	$98.20
Purchase #5	$201.25	7.337%	$216.0157	$216.02	$216.00	$216.00
Purchase #6	$80.96	5.450%	$85.3723	$85.37	$85.35	$85.40
Purchase #7	$30.35	6.607%	$32.3552	$32.36	$32.35	$32.40
7 purchase totals =	$541.19		$582.1610	$582.16	$582.10	$582.20