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	$18.66	7.843%	$20.1235	$20.12	$20.10	$20.10
Purchase #2	$237.37	13.137%	$268.5533	$268.55	$268.55	$268.60
Purchase #3	$53.72	7.693%	$57.8527	$57.85	$57.85	$57.90
Purchase #4	$47.72	12.846%	$53.8501	$53.85	$53.85	$53.90
Purchase #5	$231.59	10.780%	$256.5554	$256.56	$256.55	$256.60
Purchase #6	$182.55	3.793%	$189.4741	$189.47	$189.45	$189.50
Purchase #7	$114.90	7.792%	$123.853	$123.85	$123.85	$123.90
7 purchase totals =	$886.51		$970.2621	$970.25	$970.20	$970.50