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	$134.59	5.720%	$142.2885	$142.29	$142.30	$142.30
Purchase #2	$123.43	8.782%	$134.2696	$134.27	$134.25	$134.30
Purchase #3	$6.28	6.534%	$6.6903	$6.69	$6.70	$6.70
Purchase #4	$78.69	7.414%	$84.5241	$84.52	$84.50	$84.50
Purchase #5	$176.40	11.281%	$196.2997	$196.30	$196.30	$196.30
Purchase #6	$73.55	6.391%	$78.2506	$78.25	$78.25	$78.30
Purchase #7	$184.77	5.219%	$194.4131	$194.41	$194.40	$194.40
7 purchase totals =	$777.71		$836.7359	$836.73	$836.70	$836.80