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	$80.25	12.348%	$90.1593	$90.16	$90.15	$90.20
Purchase #2	$35.90	4.284%	$37.438	$37.44	$37.45	$37.40
Purchase #3	$27.30	8.172%	$29.531	$29.53	$29.55	$29.50
Purchase #4	$55.70	5.657%	$58.8509	$58.85	$58.85	$58.90
Purchase #5	$243.58	7.783%	$262.5378	$262.54	$262.55	$262.50
Purchase #6	$29.49	10.129%	$32.477	$32.48	$32.50	$32.50
Purchase #7	$163.36	12.496%	$183.7735	$183.77	$183.75	$183.80
7 purchase totals =	$635.58		$694.7675	$694.77	$694.80	$694.80