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	$12.58	6.402%	$13.3854	$13.39	$13.40	$13.40
Purchase #2	$21.61	12.687%	$24.3517	$24.35	$24.35	$24.40
Purchase #3	$180.30	3.169%	$186.0137	$186.01	$186.00	$186.00
Purchase #4	$172.93	13.436%	$196.1649	$196.16	$196.15	$196.20
Purchase #5	$125.57	4.708%	$131.4818	$131.48	$131.50	$131.50
Purchase #6	$104.78	3.293%	$108.2304	$108.23	$108.25	$108.20
Purchase #7	$238.98	11.860%	$267.323	$267.32	$267.30	$267.30
7 purchase totals =	$856.75		$926.9509	$926.94	$926.95	$927.00