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	$188.85	11.721%	$210.9851	$210.99	$211.00	$211.00
Purchase #2	$243.28	10.453%	$268.7101	$268.71	$268.70	$268.70
Purchase #3	$162.74	11.703%	$181.7855	$181.79	$181.80	$181.80
Purchase #4	$116.27	4.521%	$121.5266	$121.53	$121.55	$121.50
Purchase #5	$61.57	10.156%	$67.823	$67.82	$67.80	$67.80
Purchase #6	$143.99	3.397%	$148.8813	$148.88	$148.90	$148.90
Purchase #7	$85.48	5.627%	$90.29	$90.29	$90.30	$90.30
7 purchase totals =	$1,002.18		$1,090.0016	$1,090.01	$1,090.05	$1,090.00