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	$52.53	3.219%	$54.2209	$54.22	$54.20	$54.20
Purchase #2	$119.34	10.128%	$131.4268	$131.43	$131.45	$131.40
Purchase #3	$56.27	11.759%	$62.8868	$62.89	$62.90	$62.90
Purchase #4	$210.82	10.616%	$233.2007	$233.20	$233.20	$233.20
Purchase #5	$212.73	12.537%	$239.4	$239.40	$239.40	$239.40
Purchase #6	$63.32	8.786%	$68.8833	$68.88	$68.90	$68.90
Purchase #7	$27.30	3.561%	$28.2722	$28.27	$28.25	$28.30
7 purchase totals =	$742.31		$818.2907	$818.29	$818.30	$818.30