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	$87.97	13.138%	$99.5275	$99.53	$99.55	$99.50
Purchase #2	$10.90	3.868%	$11.3216	$11.32	$11.30	$11.30
Purchase #3	$104.33	11.475%	$116.3019	$116.30	$116.30	$116.30
Purchase #4	$26.82	5.483%	$28.2905	$28.29	$28.30	$28.30
Purchase #5	$83.25	11.588%	$92.897	$92.90	$92.90	$92.90
Purchase #6	$46.88	12.346%	$52.6678	$52.67	$52.65	$52.70
Purchase #7	$236.90	11.426%	$263.9682	$263.97	$263.95	$264.00
7 purchase totals =	$597.05		$664.9745	$664.98	$664.95	$665.00