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	$42.84	9.298%	$46.8233	$46.82	$46.80	$46.80
Purchase #2	$158.30	12.650%	$178.325	$178.33	$178.35	$178.30
Purchase #3	$172.37	9.319%	$188.4332	$188.43	$188.45	$188.40
Purchase #4	$65.29	7.244%	$70.0196	$70.02	$70.00	$70.00
Purchase #5	$45.25	7.815%	$48.7863	$48.79	$48.80	$48.80
Purchase #6	$41.88	9.488%	$45.8536	$45.85	$45.85	$45.90
Purchase #7	$232.39	11.608%	$259.3658	$259.37	$259.35	$259.40
7 purchase totals =	$758.32		$837.6068	$837.61	$837.60	$837.60