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	$86.32	5.290%	$90.8863	$90.89	$90.90	$90.90
Purchase #2	$144.48	9.562%	$158.2952	$158.30	$158.30	$158.30
Purchase #3	$156.27	8.640%	$169.7717	$169.77	$169.75	$169.80
Purchase #4	$168.80	8.333%	$182.8661	$182.87	$182.85	$182.90
Purchase #5	$191.44	4.781%	$200.5927	$200.59	$200.60	$200.60
Purchase #6	$239.57	8.321%	$259.5046	$259.50	$259.50	$259.50
Purchase #7	$26.31	6.720%	$28.078	$28.08	$28.10	$28.10
7 purchase totals =	$1,013.19		$1,089.9946	$1,090.00	$1,090.00	$1,090.10