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	$164.88	8.492%	$178.8816	$178.88	$178.90	$178.90
Purchase #2	$128.65	12.212%	$144.3607	$144.36	$144.35	$144.40
Purchase #3	$84.93	7.300%	$91.1299	$91.13	$91.15	$91.10
Purchase #4	$76.56	12.114%	$85.8345	$85.83	$85.85	$85.80
Purchase #5	$77.63	5.837%	$82.1613	$82.16	$82.15	$82.20
Purchase #6	$200.96	12.375%	$225.8288	$225.83	$225.85	$225.80
Purchase #7	$187.52	4.402%	$195.7746	$195.77	$195.75	$195.80
7 purchase totals =	$921.13		$1,003.9714	$1,003.96	$1,004.00	$1,004.00