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	$232.49	4.587%	$243.1543	$243.15	$243.15	$243.20
Purchase #2	$39.31	13.562%	$44.6412	$44.64	$44.65	$44.60
Purchase #3	$82.25	10.524%	$90.906	$90.91	$90.90	$90.90
Purchase #4	$19.84	5.276%	$20.8868	$20.89	$20.90	$20.90
Purchase #5	$249.90	5.427%	$263.4621	$263.46	$263.45	$263.50
Purchase #6	$109.77	12.307%	$123.2794	$123.28	$123.30	$123.30
Purchase #7	$93.77	12.498%	$105.4894	$105.49	$105.50	$105.50
7 purchase totals =	$827.33		$891.8192	$891.82	$891.85	$891.90