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	$104.55	13.217%	$118.3684	$118.37	$118.35	$118.40
Purchase #2	$234.92	3.171%	$242.3693	$242.37	$242.35	$242.40
Purchase #3	$201.81	7.104%	$216.1466	$216.15	$216.15	$216.10
Purchase #4	$90.79	9.228%	$99.1681	$99.17	$99.15	$99.20
Purchase #5	$39.36	8.303%	$42.6281	$42.63	$42.65	$42.60
Purchase #6	$41.37	13.809%	$47.0828	$47.08	$47.10	$47.10
Purchase #7	$49.55	12.753%	$55.8691	$55.87	$55.85	$55.90
7 purchase totals =	$762.35		$821.6324	$821.64	$821.60	$821.70