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	$100.77	3.757%	$104.5559	$104.56	$104.55	$104.60
Purchase #2	$141.27	10.544%	$156.1655	$156.17	$156.15	$156.20
Purchase #3	$81.52	13.702%	$92.6899	$92.69	$92.70	$92.70
Purchase #4	$81.62	9.571%	$89.4319	$89.43	$89.45	$89.40
Purchase #5	$75.76	12.745%	$85.4156	$85.42	$85.40	$85.40
Purchase #6	$73.68	3.127%	$75.984	$75.98	$76.00	$76.00
Purchase #7	$227.83	3.537%	$235.8883	$235.89	$235.90	$235.90
7 purchase totals =	$782.45		$840.1311	$840.14	$840.15	$840.20