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	$65.49	10.690%	$72.4909	$72.49	$72.50	$72.50
Purchase #2	$250.32	3.564%	$259.2414	$259.24	$259.25	$259.20
Purchase #3	$209.77	4.462%	$219.1299	$219.13	$219.15	$219.10
Purchase #4	$193.30	9.869%	$212.3768	$212.38	$212.40	$212.40
Purchase #5	$29.63	7.280%	$31.7871	$31.79	$31.80	$31.80
Purchase #6	$97.28	12.345%	$109.2892	$109.29	$109.30	$109.30
Purchase #7	$12.77	11.817%	$14.279	$14.28	$14.30	$14.30
7 purchase totals =	$858.56		$918.5943	$918.60	$918.70	$918.60