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	$51.38	5.104%	$54.0024	$54.00	$54.00	$54.00
Purchase #2	$236.97	12.150%	$265.7619	$265.76	$265.75	$265.80
Purchase #3	$62.67	12.225%	$70.3314	$70.33	$70.35	$70.30
Purchase #4	$142.32	9.805%	$156.2745	$156.27	$156.25	$156.30
Purchase #5	$136.26	11.584%	$152.0444	$152.04	$152.05	$152.00
Purchase #6	$96.90	7.284%	$103.9582	$103.96	$103.95	$104.00
Purchase #7	$65.52	13.779%	$74.548	$74.55	$74.55	$74.50
7 purchase totals =	$792.02		$876.9208	$876.91	$876.90	$876.90