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	$41.96	3.174%	$43.2918	$43.29	$43.30	$43.30
Purchase #2	$42.41	10.626%	$46.9165	$46.92	$46.90	$46.90
Purchase #3	$203.97	5.532%	$215.2536	$215.25	$215.25	$215.30
Purchase #4	$162.34	4.780%	$170.0999	$170.10	$170.10	$170.10
Purchase #5	$240.54	4.304%	$250.8928	$250.89	$250.90	$250.90
Purchase #6	$128.32	9.826%	$140.9287	$140.93	$140.95	$140.90
Purchase #7	$125.39	10.404%	$138.4356	$138.44	$138.45	$138.40
7 purchase totals =	$944.93		$1,005.8189	$1,005.82	$1,005.85	$1,005.80