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	$88.87	11.753%	$99.3149	$99.31	$99.30	$99.30
Purchase #2	$140.85	6.847%	$150.494	$150.49	$150.50	$150.50
Purchase #3	$107.95	7.323%	$115.8552	$115.86	$115.85	$115.90
Purchase #4	$177.93	10.655%	$196.8884	$196.89	$196.90	$196.90
Purchase #5	$131.98	12.420%	$148.3719	$148.37	$148.35	$148.40
Purchase #6	$232.29	10.711%	$257.1706	$257.17	$257.15	$257.20
Purchase #7	$171.62	3.122%	$176.978	$176.98	$177.00	$177.00
7 purchase totals =	$1,051.49		$1,145.0730	$1,145.07	$1,145.05	$1,145.20