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	$123.82	4.648%	$129.5752	$129.58	$129.60	$129.60
Purchase #2	$126.41	8.764%	$137.4886	$137.49	$137.50	$137.50
Purchase #3	$104.68	4.646%	$109.5434	$109.54	$109.55	$109.50
Purchase #4	$207.36	13.583%	$235.5257	$235.53	$235.55	$235.50
Purchase #5	$56.39	4.836%	$59.117	$59.12	$59.10	$59.10
Purchase #6	$90.71	3.386%	$93.7814	$93.78	$93.80	$93.80
Purchase #7	$114.85	7.868%	$123.8864	$123.89	$123.90	$123.90
7 purchase totals =	$824.22		$888.9177	$888.93	$889.00	$888.90