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	$79.72	11.696%	$89.0441	$89.04	$89.05	$89.00
Purchase #2	$66.30	7.814%	$71.4807	$71.48	$71.50	$71.50
Purchase #3	$163.71	11.196%	$182.039	$182.04	$182.05	$182.00
Purchase #4	$36.60	12.456%	$41.1589	$41.16	$41.15	$41.20
Purchase #5	$227.25	4.514%	$237.5081	$237.51	$237.50	$237.50
Purchase #6	$81.92	3.851%	$85.0747	$85.07	$85.05	$85.10
Purchase #7	$235.74	7.678%	$253.8401	$253.84	$253.85	$253.80
7 purchase totals =	$891.24		$960.1456	$960.14	$960.15	$960.10