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	$167.45	13.396%	$189.8816	$189.88	$189.90	$189.90
Purchase #2	$106.57	7.118%	$114.1557	$114.16	$114.15	$114.20
Purchase #3	$103.50	6.195%	$109.9118	$109.91	$109.90	$109.90
Purchase #4	$28.68	5.397%	$30.2279	$30.23	$30.25	$30.20
Purchase #5	$92.41	7.106%	$98.9767	$98.98	$99.00	$99.00
Purchase #6	$180.26	8.108%	$194.8755	$194.88	$194.90	$194.90
Purchase #7	$88.28	12.288%	$99.1278	$99.13	$99.15	$99.10
7 purchase totals =	$767.15		$837.1570	$837.17	$837.25	$837.20