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	$83.45	7.362%	$89.5936	$89.59	$89.60	$89.60
Purchase #2	$90.76	8.823%	$98.7678	$98.77	$98.75	$98.80
Purchase #3	$84.73	11.834%	$94.7569	$94.76	$94.75	$94.80
Purchase #4	$81.26	5.244%	$85.5213	$85.52	$85.50	$85.50
Purchase #5	$198.40	8.760%	$215.7798	$215.78	$215.80	$215.80
Purchase #6	$153.33	3.526%	$158.7364	$158.74	$158.75	$158.70
Purchase #7	$243.97	7.850%	$263.1216	$263.12	$263.10	$263.10
7 purchase totals =	$935.90		$1,006.2774	$1,006.28	$1,006.25	$1,006.30