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	$61.79	5.727%	$65.3287	$65.33	$65.35	$65.30
Purchase #2	$78.38	6.770%	$83.6863	$83.69	$83.70	$83.70
Purchase #3	$103.73	7.341%	$111.3448	$111.34	$111.35	$111.30
Purchase #4	$10.40	13.507%	$11.8047	$11.80	$11.80	$11.80
Purchase #5	$214.25	11.289%	$238.4367	$238.44	$238.45	$238.40
Purchase #6	$239.48	3.737%	$248.4294	$248.43	$248.45	$248.40
Purchase #7	$197.27	8.148%	$213.3436	$213.34	$213.35	$213.30
7 purchase totals =	$905.30		$972.3742	$972.37	$972.45	$972.20