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	$162.93	12.320%	$183.003	$183.00	$183.00	$183.00
Purchase #2	$163.44	8.532%	$177.3847	$177.38	$177.40	$177.40
Purchase #3	$38.72	4.293%	$40.3822	$40.38	$40.40	$40.40
Purchase #4	$205.25	3.126%	$211.6661	$211.67	$211.65	$211.70
Purchase #5	$83.74	6.689%	$89.3414	$89.34	$89.35	$89.30
Purchase #6	$71.53	10.362%	$78.9419	$78.94	$78.95	$78.90
Purchase #7	$236.72	10.426%	$261.4004	$261.40	$261.40	$261.40
7 purchase totals =	$962.33		$1,042.1197	$1,042.11	$1,042.15	$1,042.10