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	$109.75	12.638%	$123.6202	$123.62	$123.60	$123.60
Purchase #2	$83.90	9.522%	$91.889	$91.89	$91.90	$91.90
Purchase #3	$219.32	3.485%	$226.9633	$226.96	$226.95	$227.00
Purchase #4	$237.32	12.561%	$267.1298	$267.13	$267.15	$267.10
Purchase #5	$150.66	9.225%	$164.5584	$164.56	$164.55	$164.60
Purchase #6	$26.48	10.809%	$29.3422	$29.34	$29.35	$29.30
Purchase #7	$174.31	6.384%	$185.438	$185.44	$185.45	$185.40
7 purchase totals =	$1,001.74		$1,088.9409	$1,088.94	$1,088.95	$1,088.90