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	$64.94	4.215%	$67.6772	$67.68	$67.70	$67.70
Purchase #2	$117.45	11.565%	$131.0331	$131.03	$131.05	$131.00
Purchase #3	$89.93	4.615%	$94.0803	$94.08	$94.10	$94.10
Purchase #4	$59.71	13.545%	$67.7977	$67.80	$67.80	$67.80
Purchase #5	$114.59	4.807%	$120.0983	$120.10	$120.10	$120.10
Purchase #6	$179.89	5.219%	$189.2785	$189.28	$189.30	$189.30
Purchase #7	$144.62	12.542%	$162.7582	$162.76	$162.75	$162.80
7 purchase totals =	$771.13		$832.7233	$832.73	$832.80	$832.80