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	$246.83	4.756%	$258.5692	$258.57	$258.55	$258.60
Purchase #2	$166.38	5.440%	$175.4311	$175.43	$175.45	$175.40
Purchase #3	$235.52	13.789%	$267.9959	$268.00	$268.00	$268.00
Purchase #4	$31.59	7.256%	$33.8822	$33.88	$33.90	$33.90
Purchase #5	$224.91	11.474%	$250.7162	$250.72	$250.70	$250.70
Purchase #6	$93.84	10.552%	$103.742	$103.74	$103.75	$103.70
Purchase #7	$82.25	3.467%	$85.1016	$85.10	$85.10	$85.10
7 purchase totals =	$1,081.32		$1,175.4382	$1,175.44	$1,175.45	$1,175.40