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	$107.88	11.278%	$120.0467	$120.05	$120.05	$120.00
Purchase #2	$233.36	11.364%	$259.879	$259.88	$259.90	$259.90
Purchase #3	$6.71	7.242%	$7.1959	$7.20	$7.20	$7.20
Purchase #4	$152.82	8.844%	$166.3354	$166.34	$166.35	$166.30
Purchase #5	$168.61	7.675%	$181.5508	$181.55	$181.55	$181.60
Purchase #6	$38.67	9.668%	$42.4086	$42.41	$42.40	$42.40
Purchase #7	$205.46	11.179%	$228.4284	$228.43	$228.45	$228.40
7 purchase totals =	$913.51		$1,005.8448	$1,005.86	$1,005.90	$1,005.80