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	$101.76	9.270%	$111.1932	$111.19	$111.20	$111.20
Purchase #2	$56.55	11.406%	$63.0001	$63.00	$63.00	$63.00
Purchase #3	$39.26	10.117%	$43.2319	$43.23	$43.25	$43.20
Purchase #4	$230.50	8.867%	$250.9384	$250.94	$250.95	$250.90
Purchase #5	$66.97	8.713%	$72.8051	$72.81	$72.80	$72.80
Purchase #6	$222.29	9.656%	$243.7543	$243.75	$243.75	$243.80
Purchase #7	$53.88	10.466%	$59.5191	$59.52	$59.50	$59.50
7 purchase totals =	$771.21		$844.4421	$844.44	$844.45	$844.40