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	$26.89	7.564%	$28.924	$28.92	$28.90	$28.90
Purchase #2	$91.76	12.506%	$103.2355	$103.24	$103.25	$103.20
Purchase #3	$17.45	4.541%	$18.2424	$18.24	$18.25	$18.20
Purchase #4	$12.94	4.701%	$13.5483	$13.55	$13.55	$13.50
Purchase #5	$175.97	9.144%	$192.0607	$192.06	$192.05	$192.10
Purchase #6	$165.27	10.109%	$181.9771	$181.98	$182.00	$182.00
Purchase #7	$83.86	6.761%	$89.5298	$89.53	$89.55	$89.50
7 purchase totals =	$574.14		$627.5178	$627.52	$627.55	$627.40