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	$81.63	7.687%	$87.9049	$87.90	$87.90	$87.90
Purchase #2	$222.72	8.445%	$241.5287	$241.53	$241.55	$241.50
Purchase #3	$37.48	6.185%	$39.7981	$39.80	$39.80	$39.80
Purchase #4	$81.69	5.574%	$86.2434	$86.24	$86.25	$86.20
Purchase #5	$113.34	9.113%	$123.6687	$123.67	$123.65	$123.70
Purchase #6	$80.74	12.445%	$90.7881	$90.79	$90.80	$90.80
Purchase #7	$227.56	13.530%	$258.3489	$258.35	$258.35	$258.30
7 purchase totals =	$845.16		$928.2808	$928.28	$928.30	$928.20