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	$73.98	8.565%	$80.3164	$80.32	$80.30	$80.30
Purchase #2	$38.47	8.319%	$41.6703	$41.67	$41.65	$41.70
Purchase #3	$182.87	7.512%	$196.6072	$196.61	$196.60	$196.60
Purchase #4	$84.28	4.384%	$87.9748	$87.97	$87.95	$88.00
Purchase #5	$161.85	6.752%	$172.7781	$172.78	$172.80	$172.80
Purchase #6	$121.71	10.137%	$134.0477	$134.05	$134.05	$134.00
Purchase #7	$67.73	5.722%	$71.6055	$71.61	$71.60	$71.60
7 purchase totals =	$730.89		$785.0000	$785.01	$784.95	$785.00