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	$36.97	3.667%	$38.3257	$38.33	$38.35	$38.30
Purchase #2	$237.45	13.216%	$268.8314	$268.83	$268.85	$268.80
Purchase #3	$196.49	4.552%	$205.4342	$205.43	$205.45	$205.40
Purchase #4	$77.96	11.418%	$86.8615	$86.86	$86.85	$86.90
Purchase #5	$46.54	12.659%	$52.4315	$52.43	$52.45	$52.40
Purchase #6	$143.74	8.153%	$155.4591	$155.46	$155.45	$155.50
Purchase #7	$141.61	12.281%	$159.0011	$159.00	$159.00	$159.00
7 purchase totals =	$880.76		$966.3445	$966.34	$966.40	$966.30