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	$81.79	9.244%	$89.3507	$89.35	$89.35	$89.40
Purchase #2	$31.72	3.774%	$32.9171	$32.92	$32.90	$32.90
Purchase #3	$164.71	8.519%	$178.7416	$178.74	$178.75	$178.70
Purchase #4	$144.50	12.721%	$162.8818	$162.88	$162.90	$162.90
Purchase #5	$91.49	3.603%	$94.7864	$94.79	$94.80	$94.80
Purchase #6	$49.45	13.611%	$56.1806	$56.18	$56.20	$56.20
Purchase #7	$144.34	13.848%	$164.3282	$164.33	$164.35	$164.30
7 purchase totals =	$708.00		$779.1864	$779.19	$779.25	$779.20