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	$172.32	9.735%	$189.0954	$189.10	$189.10	$189.10
Purchase #2	$196.64	13.870%	$223.914	$223.91	$223.90	$223.90
Purchase #3	$108.65	11.162%	$120.7775	$120.78	$120.80	$120.80
Purchase #4	$135.46	12.567%	$152.4833	$152.48	$152.50	$152.50
Purchase #5	$179.58	4.129%	$186.9949	$186.99	$187.00	$187.00
Purchase #6	$123.90	12.374%	$139.2314	$139.23	$139.25	$139.20
Purchase #7	$63.79	6.664%	$68.041	$68.04	$68.05	$68.00
7 purchase totals =	$980.34		$1,080.5375	$1,080.53	$1,080.60	$1,080.50