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	$97.68	4.767%	$102.3364	$102.34	$102.35	$102.30
Purchase #2	$43.87	10.209%	$48.3487	$48.35	$48.35	$48.30
Purchase #3	$124.27	10.528%	$137.3531	$137.35	$137.35	$137.40
Purchase #4	$45.61	4.513%	$47.6684	$47.67	$47.65	$47.70
Purchase #5	$197.77	10.469%	$218.4745	$218.47	$218.45	$218.50
Purchase #6	$78.41	9.211%	$85.6323	$85.63	$85.65	$85.60
Purchase #7	$83.58	6.632%	$89.123	$89.12	$89.10	$89.10
7 purchase totals =	$671.19		$728.9364	$728.93	$728.90	$728.90