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	$71.52	9.765%	$78.5039	$78.50	$78.50	$78.50
Purchase #2	$206.87	7.474%	$222.3315	$222.33	$222.35	$222.30
Purchase #3	$119.67	11.822%	$133.8174	$133.82	$133.80	$133.80
Purchase #4	$7.82	7.615%	$8.4155	$8.42	$8.40	$8.40
Purchase #5	$217.54	8.466%	$235.9569	$235.96	$235.95	$236.00
Purchase #6	$178.87	8.666%	$194.3709	$194.37	$194.35	$194.40
Purchase #7	$170.78	11.809%	$190.9474	$190.95	$190.95	$190.90
7 purchase totals =	$973.07		$1,064.3435	$1,064.35	$1,064.30	$1,064.30