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	$249.33	4.206%	$259.8168	$259.82	$259.80	$259.80
Purchase #2	$69.72	12.537%	$78.4608	$78.46	$78.45	$78.50
Purchase #3	$212.82	10.412%	$234.9788	$234.98	$235.00	$235.00
Purchase #4	$200.84	7.153%	$215.2061	$215.21	$215.20	$215.20
Purchase #5	$53.75	7.462%	$57.7608	$57.76	$57.75	$57.80
Purchase #6	$139.27	7.819%	$150.1595	$150.16	$150.15	$150.20
Purchase #7	$7.59	10.292%	$8.3712	$8.37	$8.35	$8.40
7 purchase totals =	$933.32		$1,004.7540	$1,004.76	$1,004.70	$1,004.90