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	$42.29	11.789%	$47.2756	$47.28	$47.30	$47.30
Purchase #2	$174.90	12.205%	$196.2465	$196.25	$196.25	$196.20
Purchase #3	$214.47	8.716%	$233.1632	$233.16	$233.15	$233.20
Purchase #4	$73.46	4.802%	$76.9875	$76.99	$77.00	$77.00
Purchase #5	$167.40	6.565%	$178.3898	$178.39	$178.40	$178.40
Purchase #6	$85.55	13.165%	$96.8127	$96.81	$96.80	$96.80
Purchase #7	$174.64	8.431%	$189.3639	$189.36	$189.35	$189.40
7 purchase totals =	$932.71		$1,018.2392	$1,018.24	$1,018.25	$1,018.30