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	$67.88	12.354%	$76.2659	$76.27	$76.25	$76.30
Purchase #2	$119.89	3.332%	$123.8847	$123.88	$123.90	$123.90
Purchase #3	$41.60	8.468%	$45.1227	$45.12	$45.10	$45.10
Purchase #4	$6.83	5.551%	$7.2091	$7.21	$7.20	$7.20
Purchase #5	$145.56	8.625%	$158.1146	$158.11	$158.10	$158.10
Purchase #6	$53.86	7.463%	$57.8796	$57.88	$57.90	$57.90
Purchase #7	$151.98	8.582%	$165.0229	$165.02	$165.00	$165.00
7 purchase totals =	$587.60		$633.4995	$633.49	$633.45	$633.50