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	$115.43	13.650%	$131.1862	$131.19	$131.20	$131.20
Purchase #2	$159.35	11.787%	$178.1326	$178.13	$178.15	$178.10
Purchase #3	$74.75	10.424%	$82.5419	$82.54	$82.55	$82.50
Purchase #4	$162.37	7.595%	$174.702	$174.70	$174.70	$174.70
Purchase #5	$118.30	11.356%	$131.7341	$131.73	$131.75	$131.70
Purchase #6	$127.47	12.381%	$143.2521	$143.25	$143.25	$143.30
Purchase #7	$7.88	6.631%	$8.4025	$8.40	$8.40	$8.40
7 purchase totals =	$765.55		$849.9514	$849.94	$850.00	$849.90