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	$29.75	4.865%	$31.1973	$31.20	$31.20	$31.20
Purchase #2	$64.32	12.585%	$72.4147	$72.41	$72.40	$72.40
Purchase #3	$142.38	6.566%	$151.7287	$151.73	$151.75	$151.70
Purchase #4	$101.56	7.736%	$109.4167	$109.42	$109.40	$109.40
Purchase #5	$137.70	3.266%	$142.1973	$142.20	$142.20	$142.20
Purchase #6	$16.35	9.390%	$17.8853	$17.89	$17.90	$17.90
Purchase #7	$123.76	7.133%	$132.5878	$132.59	$132.60	$132.60
7 purchase totals =	$615.82		$657.4278	$657.44	$657.45	$657.40