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	$148.37	11.502%	$165.4355	$165.44	$165.45	$165.40
Purchase #2	$81.68	6.311%	$86.8348	$86.83	$86.85	$86.80
Purchase #3	$90.83	8.530%	$98.5778	$98.58	$98.60	$98.60
Purchase #4	$224.65	3.253%	$231.9579	$231.96	$231.95	$232.00
Purchase #5	$105.31	3.507%	$109.0032	$109.00	$109.00	$109.00
Purchase #6	$67.58	10.659%	$74.7834	$74.78	$74.80	$74.80
Purchase #7	$82.94	11.298%	$92.3106	$92.31	$92.30	$92.30
7 purchase totals =	$801.36		$858.9032	$858.90	$858.95	$858.90