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	$91.78	7.368%	$98.5424	$98.54	$98.55	$98.50
Purchase #2	$92.81	9.166%	$101.317	$101.32	$101.30	$101.30
Purchase #3	$39.66	7.155%	$42.4977	$42.50	$42.50	$42.50
Purchase #4	$102.30	6.761%	$109.2165	$109.22	$109.20	$109.20
Purchase #5	$104.40	10.496%	$115.3578	$115.36	$115.35	$115.40
Purchase #6	$103.29	11.834%	$115.5133	$115.51	$115.50	$115.50
Purchase #7	$99.73	5.340%	$105.0556	$105.06	$105.05	$105.10
7 purchase totals =	$633.97		$687.5003	$687.51	$687.45	$687.50