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	$104.33	11.554%	$116.3843	$116.38	$116.40	$116.40
Purchase #2	$250.47	10.547%	$276.8871	$276.89	$276.90	$276.90
Purchase #3	$117.71	12.464%	$132.3814	$132.38	$132.40	$132.40
Purchase #4	$99.29	13.620%	$112.8133	$112.81	$112.80	$112.80
Purchase #5	$30.58	5.802%	$32.3543	$32.35	$32.35	$32.40
Purchase #6	$174.84	12.424%	$196.5621	$196.56	$196.55	$196.60
Purchase #7	$74.98	3.580%	$77.6643	$77.66	$77.65	$77.70
7 purchase totals =	$852.20		$945.0468	$945.03	$945.05	$945.20