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	$94.56	5.638%	$99.8913	$99.89	$99.90	$99.90
Purchase #2	$175.88	3.657%	$182.3119	$182.31	$182.30	$182.30
Purchase #3	$65.49	9.775%	$71.8916	$71.89	$71.90	$71.90
Purchase #4	$89.86	12.500%	$101.0925	$101.09	$101.10	$101.10
Purchase #5	$52.63	4.435%	$54.9641	$54.96	$54.95	$55.00
Purchase #6	$65.88	10.711%	$72.9364	$72.94	$72.95	$72.90
Purchase #7	$145.68	6.594%	$155.2861	$155.29	$155.30	$155.30
7 purchase totals =	$689.98		$738.3739	$738.37	$738.40	$738.40