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	$213.59	5.405%	$225.1345	$225.13	$225.15	$225.10
Purchase #2	$96.89	12.316%	$108.823	$108.82	$108.80	$108.80
Purchase #3	$102.48	11.795%	$114.5675	$114.57	$114.55	$114.60
Purchase #4	$66.58	9.209%	$72.7114	$72.71	$72.70	$72.70
Purchase #5	$62.75	9.380%	$68.636	$68.64	$68.65	$68.60
Purchase #6	$98.35	7.595%	$105.8197	$105.82	$105.80	$105.80
Purchase #7	$146.58	6.508%	$156.1194	$156.12	$156.10	$156.10
7 purchase totals =	$787.22		$851.8115	$851.81	$851.75	$851.70