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	$132.72	7.377%	$142.5108	$142.51	$142.50	$142.50
Purchase #2	$113.55	11.156%	$126.2176	$126.22	$126.20	$126.20
Purchase #3	$142.69	6.644%	$152.1703	$152.17	$152.15	$152.20
Purchase #4	$181.77	5.621%	$191.9873	$191.99	$192.00	$192.00
Purchase #5	$61.38	3.179%	$63.3313	$63.33	$63.35	$63.30
Purchase #6	$66.57	8.214%	$72.0381	$72.04	$72.05	$72.00
Purchase #7	$250.79	11.695%	$280.1199	$280.12	$280.10	$280.10
7 purchase totals =	$949.47		$1,028.3753	$1,028.38	$1,028.35	$1,028.30