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	$52.59	13.240%	$59.5529	$59.55	$59.55	$59.60
Purchase #2	$42.76	3.762%	$44.3686	$44.37	$44.35	$44.40
Purchase #3	$242.74	10.807%	$268.9729	$268.97	$268.95	$269.00
Purchase #4	$245.30	3.242%	$253.2526	$253.25	$253.25	$253.30
Purchase #5	$11.98	7.292%	$12.8536	$12.85	$12.85	$12.90
Purchase #6	$87.36	13.619%	$99.2576	$99.26	$99.25	$99.30
Purchase #7	$181.69	3.868%	$188.7178	$188.72	$188.70	$188.70
7 purchase totals =	$864.42		$926.9760	$926.97	$926.90	$927.20