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	$132.85	6.258%	$141.1638	$141.16	$141.15	$141.20
Purchase #2	$231.89	6.142%	$246.1327	$246.13	$246.15	$246.10
Purchase #3	$61.53	10.478%	$67.9771	$67.98	$68.00	$68.00
Purchase #4	$83.86	12.292%	$94.1681	$94.17	$94.15	$94.20
Purchase #5	$132.77	3.831%	$137.8564	$137.86	$137.85	$137.90
Purchase #6	$189.75	13.604%	$215.5636	$215.56	$215.55	$215.60
Purchase #7	$64.86	9.612%	$71.0943	$71.09	$71.10	$71.10
7 purchase totals =	$897.51		$973.9560	$973.95	$973.95	$974.10