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	$115.57	6.796%	$123.4241	$123.42	$123.40	$123.40
Purchase #2	$223.30	4.164%	$232.5982	$232.60	$232.60	$232.60
Purchase #3	$35.74	7.841%	$38.5424	$38.54	$38.55	$38.50
Purchase #4	$79.95	7.582%	$86.0118	$86.01	$86.00	$86.00
Purchase #5	$29.39	12.807%	$33.154	$33.15	$33.15	$33.20
Purchase #6	$197.46	13.165%	$223.4556	$223.46	$223.45	$223.50
Purchase #7	$204.60	13.343%	$231.8998	$231.90	$231.90	$231.90
7 purchase totals =	$886.01		$969.0859	$969.08	$969.05	$969.10