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	$74.72	10.602%	$82.6418	$82.64	$82.65	$82.60
Purchase #2	$42.63	12.451%	$47.9379	$47.94	$47.95	$47.90
Purchase #3	$22.38	13.102%	$25.3122	$25.31	$25.30	$25.30
Purchase #4	$162.41	3.652%	$168.3412	$168.34	$168.35	$168.30
Purchase #5	$66.31	13.608%	$75.3335	$75.33	$75.35	$75.30
Purchase #6	$78.51	13.155%	$88.838	$88.84	$88.85	$88.80
Purchase #7	$171.59	5.533%	$181.0841	$181.08	$181.10	$181.10
7 purchase totals =	$618.55		$669.4887	$669.48	$669.55	$669.30