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	$13.30	11.765%	$14.8647	$14.86	$14.85	$14.90
Purchase #2	$181.71	6.106%	$192.8052	$192.81	$192.80	$192.80
Purchase #3	$99.93	13.155%	$113.0758	$113.08	$113.10	$113.10
Purchase #4	$38.45	12.700%	$43.3332	$43.33	$43.35	$43.30
Purchase #5	$79.33	8.426%	$86.0143	$86.01	$86.00	$86.00
Purchase #6	$224.77	12.700%	$253.3158	$253.32	$253.30	$253.30
Purchase #7	$116.42	12.508%	$130.9818	$130.98	$131.00	$131.00
7 purchase totals =	$753.91		$834.3908	$834.39	$834.40	$834.40