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	$99.77	4.338%	$104.098	$104.10	$104.10	$104.10
Purchase #2	$241.46	13.288%	$273.5452	$273.55	$273.55	$273.50
Purchase #3	$67.91	5.400%	$71.5771	$71.58	$71.60	$71.60
Purchase #4	$33.96	12.108%	$38.0719	$38.07	$38.05	$38.10
Purchase #5	$88.81	6.761%	$94.8144	$94.81	$94.80	$94.80
Purchase #6	$243.46	9.753%	$267.2047	$267.20	$267.20	$267.20
Purchase #7	$70.26	3.190%	$72.5013	$72.50	$72.50	$72.50
7 purchase totals =	$845.63		$921.8126	$921.81	$921.80	$921.80