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	$170.77	5.686%	$180.48	$180.48	$180.50	$180.50
Purchase #2	$142.27	5.235%	$149.7178	$149.72	$149.70	$149.70
Purchase #3	$137.69	7.601%	$148.1558	$148.16	$148.15	$148.20
Purchase #4	$150.28	10.238%	$165.6657	$165.67	$165.65	$165.70
Purchase #5	$153.90	8.443%	$166.8938	$166.89	$166.90	$166.90
Purchase #6	$27.31	13.815%	$31.0829	$31.08	$31.10	$31.10
Purchase #7	$232.45	12.437%	$261.3598	$261.36	$261.35	$261.40
7 purchase totals =	$1,014.67		$1,103.3558	$1,103.36	$1,103.35	$1,103.50