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	$52.62	8.479%	$57.0816	$57.08	$57.10	$57.10
Purchase #2	$117.48	11.783%	$131.3227	$131.32	$131.30	$131.30
Purchase #3	$29.60	3.385%	$30.602	$30.60	$30.60	$30.60
Purchase #4	$98.48	7.250%	$105.6198	$105.62	$105.60	$105.60
Purchase #5	$171.43	4.551%	$179.2318	$179.23	$179.25	$179.20
Purchase #6	$187.75	13.737%	$213.5412	$213.54	$213.55	$213.50
Purchase #7	$165.61	3.534%	$171.4627	$171.46	$171.45	$171.50
7 purchase totals =	$822.97		$888.8618	$888.85	$888.85	$888.80