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	$81.99	4.391%	$85.5902	$85.59	$85.60	$85.60
Purchase #2	$85.49	4.776%	$89.573	$89.57	$89.55	$89.60
Purchase #3	$38.72	8.346%	$41.9516	$41.95	$41.95	$42.00
Purchase #4	$163.40	7.582%	$175.789	$175.79	$175.80	$175.80
Purchase #5	$200.91	8.792%	$218.574	$218.57	$218.55	$218.60
Purchase #6	$170.59	8.818%	$185.6326	$185.63	$185.65	$185.60
Purchase #7	$36.31	9.459%	$39.7446	$39.74	$39.75	$39.70
7 purchase totals =	$777.41		$836.8550	$836.84	$836.85	$836.90