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	$235.44	5.387%	$248.1232	$248.12	$248.10	$248.10
Purchase #2	$61.68	10.802%	$68.3427	$68.34	$68.35	$68.30
Purchase #3	$203.32	10.397%	$224.4592	$224.46	$224.45	$224.50
Purchase #4	$74.45	12.689%	$83.897	$83.90	$83.90	$83.90
Purchase #5	$78.89	3.236%	$81.4429	$81.44	$81.45	$81.40
Purchase #6	$203.54	9.520%	$222.917	$222.92	$222.90	$222.90
Purchase #7	$82.58	10.475%	$91.2303	$91.23	$91.25	$91.20
7 purchase totals =	$939.90		$1,020.4123	$1,020.41	$1,020.40	$1,020.30