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	$28.87	8.858%	$31.4273	$31.43	$31.45	$31.40
Purchase #2	$99.63	6.720%	$106.3251	$106.33	$106.35	$106.30
Purchase #3	$139.28	6.214%	$147.9349	$147.93	$147.95	$147.90
Purchase #4	$119.82	10.119%	$131.9446	$131.94	$131.95	$131.90
Purchase #5	$173.54	13.307%	$196.633	$196.63	$196.65	$196.60
Purchase #6	$118.64	3.828%	$123.1815	$123.18	$123.20	$123.20
Purchase #7	$48.70	3.568%	$50.4376	$50.44	$50.45	$50.40
7 purchase totals =	$728.48		$787.8840	$787.88	$788.00	$787.70