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	$231.67	7.720%	$249.5549	$249.55	$249.55	$249.60
Purchase #2	$153.50	9.327%	$167.8169	$167.82	$167.80	$167.80
Purchase #3	$35.79	7.106%	$38.3332	$38.33	$38.35	$38.30
Purchase #4	$31.78	12.799%	$35.8475	$35.85	$35.85	$35.80
Purchase #5	$39.63	9.236%	$43.2902	$43.29	$43.30	$43.30
Purchase #6	$100.78	12.623%	$113.5015	$113.50	$113.50	$113.50
Purchase #7	$190.44	13.393%	$215.9456	$215.95	$215.95	$215.90
7 purchase totals =	$783.59		$864.2898	$864.29	$864.30	$864.20