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	$248.27	4.145%	$258.5608	$258.56	$258.55	$258.60
Purchase #2	$212.76	7.170%	$228.0149	$228.01	$228.00	$228.00
Purchase #3	$115.29	13.741%	$131.132	$131.13	$131.15	$131.10
Purchase #4	$60.42	11.404%	$67.3103	$67.31	$67.30	$67.30
Purchase #5	$145.56	12.676%	$164.0112	$164.01	$164.00	$164.00
Purchase #6	$25.72	4.287%	$26.8226	$26.82	$26.80	$26.80
Purchase #7	$90.97	13.271%	$103.0426	$103.04	$103.05	$103.00
7 purchase totals =	$898.99		$978.8944	$978.88	$978.85	$978.80