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	$250.68	11.430%	$279.3327	$279.33	$279.35	$279.30
Purchase #2	$206.56	6.127%	$219.2159	$219.22	$219.20	$219.20
Purchase #3	$121.46	13.857%	$138.2907	$138.29	$138.30	$138.30
Purchase #4	$189.39	10.628%	$209.5184	$209.52	$209.50	$209.50
Purchase #5	$77.39	10.568%	$85.5686	$85.57	$85.55	$85.60
Purchase #6	$40.34	12.477%	$45.3732	$45.37	$45.35	$45.40
Purchase #7	$184.54	8.667%	$200.5341	$200.53	$200.55	$200.50
7 purchase totals =	$1,070.36		$1,177.8336	$1,177.83	$1,177.80	$1,177.80