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	$135.33	9.561%	$148.2689	$148.27	$148.25	$148.30
Purchase #2	$243.39	9.216%	$265.8208	$265.82	$265.80	$265.80
Purchase #3	$50.98	6.868%	$54.4813	$54.48	$54.50	$54.50
Purchase #4	$28.93	10.826%	$32.062	$32.06	$32.05	$32.10
Purchase #5	$51.61	3.372%	$53.3503	$53.35	$53.35	$53.40
Purchase #6	$140.48	5.553%	$148.2809	$148.28	$148.30	$148.30
Purchase #7	$85.74	13.708%	$97.4932	$97.49	$97.50	$97.50
7 purchase totals =	$736.46		$799.7574	$799.75	$799.75	$799.90