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	$17.57	4.493%	$18.3594	$18.36	$18.35	$18.40
Purchase #2	$84.71	13.639%	$96.2636	$96.26	$96.25	$96.30
Purchase #3	$68.48	5.707%	$72.3882	$72.39	$72.40	$72.40
Purchase #4	$120.41	11.369%	$134.0994	$134.10	$134.10	$134.10
Purchase #5	$172.83	11.617%	$192.9077	$192.91	$192.90	$192.90
Purchase #6	$141.40	7.433%	$151.9103	$151.91	$151.90	$151.90
Purchase #7	$179.32	5.337%	$188.8903	$188.89	$188.90	$188.90
7 purchase totals =	$784.72		$854.8189	$854.82	$854.80	$854.90