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	$125.77	4.332%	$131.2184	$131.22	$131.20	$131.20
Purchase #2	$25.66	9.196%	$28.0197	$28.02	$28.00	$28.00
Purchase #3	$223.72	3.511%	$231.5748	$231.57	$231.55	$231.60
Purchase #4	$162.77	11.407%	$181.3372	$181.34	$181.35	$181.30
Purchase #5	$121.60	4.620%	$127.2179	$127.22	$127.20	$127.20
Purchase #6	$11.28	4.656%	$11.8052	$11.81	$11.80	$11.80
Purchase #7	$38.77	10.303%	$42.7645	$42.76	$42.75	$42.80
7 purchase totals =	$709.57		$753.9377	$753.94	$753.85	$753.90