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	$37.72	13.822%	$42.9337	$42.93	$42.95	$42.90
Purchase #2	$170.44	10.754%	$188.7691	$188.77	$188.75	$188.80
Purchase #3	$63.37	10.795%	$70.2108	$70.21	$70.20	$70.20
Purchase #4	$84.30	13.672%	$95.8255	$95.83	$95.85	$95.80
Purchase #5	$188.60	10.529%	$208.4577	$208.46	$208.45	$208.50
Purchase #6	$215.83	10.697%	$238.9173	$238.92	$238.90	$238.90
Purchase #7	$77.59	7.512%	$83.4186	$83.42	$83.40	$83.40
7 purchase totals =	$837.85		$928.5327	$928.54	$928.50	$928.50