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	$90.87	11.556%	$101.3709	$101.37	$101.35	$101.40
Purchase #2	$79.76	4.367%	$83.2431	$83.24	$83.25	$83.20
Purchase #3	$26.49	10.213%	$29.1954	$29.20	$29.20	$29.20
Purchase #4	$105.64	13.490%	$119.8908	$119.89	$119.90	$119.90
Purchase #5	$84.31	9.726%	$92.51	$92.51	$92.50	$92.50
Purchase #6	$33.88	12.813%	$38.221	$38.22	$38.20	$38.20
Purchase #7	$73.27	5.783%	$77.5072	$77.51	$77.50	$77.50
7 purchase totals =	$494.22		$541.9384	$541.94	$541.90	$541.90