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	$238.69	12.412%	$268.3162	$268.32	$268.30	$268.30
Purchase #2	$81.49	6.199%	$86.5416	$86.54	$86.55	$86.50
Purchase #3	$27.55	8.440%	$29.8752	$29.88	$29.90	$29.90
Purchase #4	$95.31	4.404%	$99.5075	$99.51	$99.50	$99.50
Purchase #5	$150.60	8.746%	$163.7715	$163.77	$163.75	$163.80
Purchase #6	$162.72	11.467%	$181.3791	$181.38	$181.40	$181.40
Purchase #7	$191.91	10.321%	$211.717	$211.72	$211.70	$211.70
7 purchase totals =	$948.27		$1,041.1081	$1,041.12	$1,041.10	$1,041.10